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Personality and cognitive aging: are positive traits protective?

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Personality and cognitive aging: are positive traits protective?

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PERSONALITY AND COGNITIVE AGING: ARE POSITIVE TRAITS
PROTECTIVE?

by

Emily Anne Schoenhofen

A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF ARTS
(PSYCHOLOGY)

August 2007

Copyright 2007 Emily Anne Schoenhofen

ii
Acknowledgements

Special thanks are given to Margaret Gatz, PhD, my advisor. I thank her for
insight, advice, and encouragement throughout this research project. I also extend my
sincere gratitude to Chandra Reynolds, PhD for being so giving of her valuable time as
well as her statistical knowledge. Additional thanks are extended to my labmates Maggi
Mackintosh, Poorni Otilingam, Randi Jones, Jessica Brommelhoff, Amber Watts, Patricia
George, and Lewina Lee for their invaluable contributions and support. And finally, I
thank my husband-to-be, Chester Sharp, for his constant support, optimism, and love.

iii
Table of Contents

Acknowledgements ii

List of Tables iv

List of Figures vi

Abstract viii

Chapter 1: Introduction 1

Chapter 2: Background 4

Chapter 3: Research Method 14

Chapter 4: Statistical Method 22

Chapter 5: Results 26

Chapter 6: Discussion 55

References 63

Appendix A 75

Appendix B 76

iv
List of Tables

Table 1: Correlations between personality traits and 18
cognitive tasks across measurement occasions.

Table 2: Ns and ages of participants who had at least 27
one cognitive measurement.

Table 3: Means, standard deviations and range 27
for personality traits.

Table 4: Means and standard deviations for cognitive 28
measures at five measurement points.

Table 5: Correlations between personality traits 29
and covariates.

Table 6: Number of individuals with cognitive 30
measurements from 1 time point to all 5 time points.

Table 7: Crosstabulation of individuals with cognitive 30
data from each IPT measurement occasion

Table 8: Females: Relation of personality traits to 36
change in cognitive functioning as measured by the
Block Design task, controlling for education.

Table 9: Females: Relation of personality traits to 37
change in cognitive functioning as measured by the
Information task, controlling for education.

Table 10: Females: Relation of personality traits to 38
change in cognitive functioning as measured by the
Digit Span task, controlling for education.

Table 11: Females: Relation of personality traits to 49
change in cognitive functioning as measured by the
Thurstone’s Memory task, controlling for education.

Table 12: Females: Relation of personality traits to 40
change in cognitive functioning as measured by the
Symbol Digit task, controlling for education.

v
Table 13: Males: Relation of personality traits to 45
change in cognitive functioning as measured by
the Block Design task, controlling for education.

Table 14: Males: Relation of personality traits to 46
change in cognitive functioning as measured by
the Information task, controlling for education.

Table 15: Males: Relation of personality traits to 47
change in cognitive functioning as measured by the
Digit Span task, controlling for education.

Table 16: Males: Relation of personality traits to 48
change in cognitive functioning as measured by
Thurstone’s Memory task, controlling for education.

Table 17: Males: Relation of personality traits to 49
change in cognitive functioning as measured by
the Symbol Digit task, controlling for education.

vi
List of Figures

Figure 1: Latent Growth Curve Model 24

Figure 2a: A random sample of trajectories 31
on Block Design for Females.

Figure 2b: A random sample of trajectories 31
on Block Design for Males.

Figure 3a: A random sample of trajectories 32
on Information for Females

Figure 3b: A random sample of trajectories 32
on Information for Males

Figure 4a: A random sample of trajectories 33
on Digit Span for Females.

Figure 4b: A random sample of trajectories 33
on Digit Span for Males.

Figure 5a: A random sample of trajectories 34
on Thurstone’s Memory for Females.

Figure 5b: A random sample of trajectories 34
on Thurstone’s Memory for Males.

Figure 6a: A random sample of trajectories 35
on Symbol Digit for Females.

Figure 6b: A random sample of trajectories 35
on Symbol Digit for Males.

Figure 7: Main effects of Openness to Experience 42
across each cognitive task over three age intervals
(55, 65, and 75) for females, controlling for education.

Figure 8: Females who endorsed higher levels of 42
Openness performed better on the Thurstone’s Memory
task before age 65 and had slower rates of decline.

vii
Figure 9: Females who endorsed higher levels of 43
Openness to Experience on Block Design had an advantage
for level of performance, but had faster rates of decline.

Figure 10: Females who endorsed higher levels of 44
Optimism initially performed better on the Thurstone’s
Memory task before age 65 but had faster rates of decline.

Figure 11: Females who endorsed higher levels of 44
Conscientiousness had an advantage on the Symbol Digit
task before age 65 had a faster rate of decline.

Figure 12: Main effects of Openness to Experience across 50
each cognitive task over three age intervals (55, 65, and 75)
for males, controlling for education.

Figure 13: Males who endorsed higher levels of Optimism 51
performed more poorly on the Block Design task at the
centering age of 65 (main effect only).

Figure 14: Males who endorsed higher levels of 51
Conscientiousness performed more poorly on the Block
Design task at the centering age of 65 (main effect only).

Figure 15: Males who endorsed higher levels of 52
Conscientiousness performed more poorly on the
Information task but had slower rates of decline than
individuals endorsing lower levels of Conscientiousness.

Figure 16: Males who endorsed higher levels of Optimism 52
performed more poorly on the Information task but had
slower rates of decline than individuals endorsing lower
levels of Optimism (nonlinear effect on slope).

Figure 17: Males who endorsed higher levels of 53
Agreeableness performed more poorly on the Information
task at the centering age of 65 (main effect only).

Figure 18: Males who endorsed higher levels of 53
Agreeableness had an advantage prior to age 65 in
performance on Symbol Digit but had a faster rate
of decline (linear effect on slope).

viii
Abstract
The purpose of this study was to examine whether personality traits affect
cognitive functioning and rate of cognitive decline in older adults. Participants were 857
individuals from the Swedish Twin/ Adoption Study of Aging (SATSA). Data included
four personality measures and longitudinal cognitive measurements. It was hypothesized
that individuals who endorsed higher levels of conscientiousness, openness, and
optimism would have higher cognitive test scores and lesser rates of cognitive decline,
whereas agreeableness would not protect against cognitive decline. Latent growth curve
models were fit to assess level of cognitive performance (intercept) and trajectories of
cognitive performance over advancing age (slope). As predicted, higher levels of
openness to experience were associated with a significantly higher performance across all
cognitive tests for both males and females even after controlling for education.
Agreeableness, as expected, but also conscientiousness and optimism, did not confer any
consistent advantage on either cognitive performance or cognitive decline.

1
Chapter 1: Introduction
It has been suggested that there are three critical components of successful aging,
a low risk for disease, maintenance of high cognitive and physical functioning and an
active engagement in life (Rowe & Kahn, 1997). Centenarians, considered prototypes of
successful aging, have been found to exemplify many of these characteristics (Evert,
Lawler, Bogan & Perls, 2003; Perls, 2004). Researchers who investigate successful aging
also describe centenarians as having had personalities associated with an optimistic,
positive attitude and a basic “enthusiasm for life” (T. Perls, personal communication,
Feburary 5, 2006). Although ancedotal evidence, such observations suggest that certain
personality factors may contribute a long-term advantage for successful aging. Currently,
little research has investigated the relationship between positive personality traits and
cognitive aging. The purpose of the current study was to examine how positive
personality traits might affect cognitive aging in the second half of the lifespan.
In general, personality traits contribute substantially to the degree to which an
individual engages in, experiences, and benefits from life. In relation to Rowe and Kahn’s
components of successful aging, recent research has suggested that an active engagement
with life via social and lesiure activities is associated with both a greater survival
(Bygren, Konlaan, & Joahansson, 1996; Glass, Mendes de Leon, Marottoli & Berkman,
2001) and a decreased risk for dementia (Crowe, Andel, Pedersen, Johanson, & Gatz,
2003; Newson, & Kemps, 2005; Wang, Karp, Winblad, & Fratiglioni, 2002; Wang et al.,
2006; Wilson, Mendes de Leon et al., 2002; Wilson, Bennett et al., 2003). In a review of
the active engagement hypothesis, Fratiglioni, Paillard-Borg, and Winblad (2004)

2
described serveral potential mechanisms that may explain the relationship between
engagement activites and cognitive decline. Of particular interest to the present study
were the cognitive reserve hypothesis and the stress hypothesis.
The cognitive reserve hypothesis posits that build up of cognitive resources can
increase compensatory abilities by using preexisting cognitive strategies against the
deleterious effects of aging on the brain (Stern, 2002, 2003, 2004; Vance & Crowe,
2006). The theory stems from findings indicating an inconsistent relationship between the
amount of brain deterioration or pathology and the amount of expressed impairment
(Katzman et al., 1988). Higher levels of cognitive reserve have been operationalized with
years of education, type of occupation, and measures of intellectual capacity earlier in
life. Research has demonstrated that individuals with higher levels of intellectual capacity
and more years of education were at a reduced risk for cognitive impairment and
dementia compared to individuals without these cognitive advantages (Albert, Jones,
Savage, & Berkman, 1995; Christiansen et al., 1999; Gatz et al., 2001; Katzman, 1993;
Leibovici, Ritchie, Ledesert, & Touchon, 1996). Lending further support to this theory,
intellectual complexity of occupation has also been found to be a protective factor against
Alzheimer’s disease, such that a higher complexity of lifetime occupational work with
people has been associated with a reduced risk of Alzheimer’s disease and all other
dementias (Andel et al., 2005). Furthermore, childhood personality traits have been found
to be associated with both academic attainment and work competence (Digman, 1972;
1989; Shiner, Masten & Roberts, 2003). We extend these findings to suggest that certain
personality features may be associated with the maintenance of higher cognitive

3
functioning via a predisposition to actively engage in or seek out cognitively stimulating
activities across the life span.
Findings from the health literature have widely suggested personality traits to be
related to physical health outcomes via disease onset, course, and coping. Specific
personality traits, such as neuroticism and hostility have been consistently associated with
risks relating to the cardiovascular system (Booth-Kewley & Freidman, 1987; Friedman
& Booth-Kewley, 1989; Smith, Glazer, Ruiz, & Gallo, 2004). In contrast, traits such as
conscientiousness, curiosity, hope, and optimism have been found to be protective against
cardiovascular disease (Giltay, Geleijnse, Zitman, Hoekstra, & Schouten, 2004; Giltay,
Kamphuis, Kalmijn, Zitman, & Kromhout, 2006), diabetes and hypertension (Richman et
al., 2005), pulmonary disease, (Kubzanksy et al., 2002) and even death (Friedman,
Tucker, Tomlinson-Keasy, & Schwartz, 1993; Swan & Carmelli, 1996). These latter
findings suggest that personality may have significant protective effects on physical
health.
The protective effects of personality have been associated with the stress-
reduction hypothesis. The stress-reduction hypothesis suggests that high level, chronic
stress is associated with negative outcomes like decreases in immune-functioning, which
in turn, may lead to an increased risk for illness and disease. Certain personality traits
have been suggested to reduce stress and may therefore lower an individual’s
suceptibility to negative health outcomes (Giltay, Geleijnse, Zitman, Hoekstra &
Schouten, 2004; Kubzansky, Sparrow, Vokonas & Kawachi, 2001). Although personality

4
has been widely studied in the physcial health literature, disporportionately less research
has examined the role of personality and cognitive health.
Chapter 2: Background
Personality and Cognition
The relationship between personality factors and cognition has been widely
studied in young and middle-aged adults; however, few studies have extended this
research to explore the role of personality in cognitive functioning and decline in the
second half of the lifespan. The majority of literature on personality and cognition has
examined the effects of neuroticism on cognitive functioning. In a cross-sectional study
of an elderly community sample, Jorm et al. (1993) found that for men, higher
neuroticism predicted poorer performance on information-processing, episodic memory
and a measure of global cognitive functioning. For women, higher neuroticism predicted
slower reaction times. In a prospective study of a cohort of older Catholic clergy
members, Wilson et al. (2003) found that individuals endorsing higher levels of
neuroticism (90th percentile) were at a two times greater risk for Alzheimer’s disease
than those low on neuroticism (10th percentile). Wilson et al. (2005) replicated and
extended these findings in a study exploring neuroticism in a large biracial elderly
community sample. At 3- and 6-year follow-up, there was a doubled risk for Alzheimer’s
disease in individuals high on neuroticism (90th percentile). Most recently, Wilson et al.
(2006) extracted data from the Rush Memory and Aging Project on a sample of older
persons without dementia at baseline who participated in annual cognitive evaluations
over a period of 3 years. Results from Cox proportional hazards models indicated that

5
individuals endorsing higher levels of neuroticism (90th percentile) were at a 2.7 times
greater risk for developing AD compared to those low on neuroticism (10th percentile).
Results from mixed-effects regression models suggested that individuals higher on
neuroticism had both a lower level of cognition at baseline and a steeper trajectory of
cognitive decline longitudinally.
In a study of personality and cognitive impairment, Crowe, Andel, Pedersen,
Fratigilioni, and Gatz (2006) examined the relationship of extraversion and neuroticism
to cognitive impairment in a sample of elderly Swedish Twins. This study utilized both a
case-control and co-twin control designs. A unique feature of this study was that
personality scores were extracted from data collected during middle adulthood, 25 years
prior to cognitive evaluations. Results from the case-control study indicated that higher
neuroticism was associated with a significantly increased risk for cognitive impairment
(controlling for age, sex, and education), while moderate extraversion was protective, and
both the combination of high neuroticism coupled with high extraversion and high
neuroticism coupled with low extraversion were associated with a greater risk for
cognitive impairment. Results from the co-twin control study found that neuroticism
alone was not a predictor of cognitive impairment, but that moderate extraversion
remained significantly protective and the combination of high neuroticism coupled with
low extraversion was associated with a significantly greater risk of cognitive impairment.
Other research has found a more nuanced relationship between neuroticism and
cognitive performance. Jelicic et al. (2003) examined the relationship between
neuroticism and cognitive performance both cross-sectionally and longitudinally in a

6
sample of adults aged 50 years and older. Results from both analyses indicated that
differences in level of neuroticism were unrelated to cognitive performance. In a cross-
sectional study of a population-based community sample of older adults, Booth, Schinka,
Brown, Mortimer, and Borenstein (2006) found that higher neuroticism predicted a
poorer performance on tasks of executive functioning and verbal learning. Despite these
findings, the authors surprisingly concluded that there was insufficient evidence to
consider neuroticism a risk factor for cognitive performance.
While a handful of studies have examined the relationship between neuroticism
and cognition, fewer studies have examined whether positive personality traits may be
protective against cognitive aging and decline. As described above, the Crowe et al.
(2006) results support the significance of moderate extraversion as protective. Structural
equation modeling of data from the MacArthur Studies of Successful Aging indicated
that men, who had stronger self-efficacy at baseline, evidenced better performance on
tasks of verbal memory than those endorsing less self-efficacy. In contrast, no protective
effects were found for women (Seeman, McAvay, Merril, Albert, & Rodin, 1996). This
study had previously determined that men and women differed on study constructs, and
so modeled men and women separately. In general, the MacArthur Studies included only
high-functioning older adults, limiting the ability to extrapolate these findings to the
broader older adult population. In the Seattle Longitudinal Study, Schaie et al. (2004)
examined the relationship between 13 factor-analyzed traits from the 75-item Test of
Behavioral Rigidity (TBR; Schaie & Parham, 1975) and the five-factor traits of
neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness

7
(NEO-PI; Costa & McCrae, 1985) on cognitive scores at baseline and longitudinally.
Results indicated that openness (NEO-PI), untroubled adequacy, low conservatism, and
low group dependency factors (all from the TBR) were most consistently related to
higher performance on cognitive tasks. Importantly, this study provided further evidence
of the stability of personality traits over a period of up to 35 years. In their conclusions,
Schaie and colleagues specifically recommended that future aging and cognition studies
include personality traits as potential predictors of cognitive performance.
Recently, a large scale review by the National Institute of Health’s Committee for
Cognitive and Emotional Health, noted the critical need for more research investigating
the relationship between psychosocial factors and cognitive health across advancing age.
This review identified only two longitudinal aging studies (Lee, Kawachi, & Grodstein,
2004 and Seeman et al., 1996) that met inclusion criteria (e.g. sample demographics and
study design) and explored the relationship between personality and cognitive outcomes
(Hendrie et al., 2006).
The current study advances the literature by examining the impact of a selection
of positive personality traits on both cognitive performance and cognitive trajectories
assessed via longitudinal models of change. Openness to experience, optimism,
conscientiousness, and agreeableness were selected as the personality traits of interest.
Although, for the purpose of this study, these traits were collectively termed “positive”, it
was not predicted that each of these traits would have an equally positive or protective
effect on cognitive health. The following sections describe each personality trait of
interest and the relevant research on the relationship with cognitive performance.

8
Openness to Experience. Openness to experience is described as an intrinsic wish
for knowledge, curiosity, and the ability to assimilate novel ideas. Closed individuals are
more rigid in their beliefs and less emotionally involved with experiences (Costa &
McCrae, 1992). Openness has been found to be highly correlated with cognitive ability
and encompasses a basic curiosity and receptivity to intellectual experience (McCrae,
1994). The personality trait of openness was selected as it seemed to best represent the
qualities that might lead to an active and cognitively stimulating engagement with life,
which in turn, may lead to a decreased risk for cognitive decline.
Findings from the Seattle Longitudinal Study found that openness was
consistently predictive of higher cognitive performances across tasks. In addition, the
relationship between level of openness and cognitive performance remained constant
across all testing intervals, suggesting the relationship between openness and cognitive
performance is very stable (Schaie et al., 2004). Baker and Bischel (2006) examined the
relationship between openness and cognitive performance in a sample divided into three
groups based on age and cognitive ability: Young (cognitively intact group of adults aged
19-60), Comparable Old (aged 61-89 who were cognitively comparable to the young
group), and Superior Old (aged 61-89 who were cognitively superior to the young group).
Results suggested that openness was only predictive of better scores for auditory
processing ability in the Comparable Old and visual spatial ability in the Superior Old.
Openness was not related to fluid reasoning, comprehension-knowledge, processing
speed, or short or long-term memory. In contrast, Booth and colleagues (2006) found that
openness was positively correlated across all indices of verbal memory and general

9
cognitive ability. The authors suggested that openness might represent a predisposition
for life-long learning and cognitive activity that is related to cognitive functioning in later
life.
It was hypothesized that individuals with higher openness would be most actively
engaged, which would be protective against declines in cognitive functioning. It was
expected that higher openness would be associated with higher performances on
cognitive tasks and slower rates of decline in cognitive performance over advancing age.
Optimism. Optimism is thought of as a global tendency to believe that one will
generally experience good versus bad outcomes in life and was originally conceptualized
as protective of health (Scheier & Carver, 1985). Optimists are more likely to see the
“silver-lining” in bad events and view downturns in life as transient, unavoidable mishaps
that are not attributed to intrinsic or personal flaws. While no research was found linking
optimism and cognitive aging, optimism has been studied more broadly in the health
literature. Optimism has been found to be related to indices of general well-being and
health (Ryff & Singer, 1998). In prospective studies, higher optimism was found to be
related to fewer medical complications after coronary bypass surgery (Scheier et al.,
1989; 1999), angioplasty (Helgeson & Fitz, 1999), and was also related to a slower
progression of atherosclerosis (Mathews et al., 2004). Furthermore, higher optimism has
been associated with better coping in individuals with Parkinson’s disease and multiple
sclerosis (de Ridder, Schreurs, & Bensing, 2000). The link between optimism and better
health outcomes has been related to the stress-reduction or moderation hypothesis.
Chronic stress has been identified as a critical antagonist to physical and mental well-

10
being and is a risk factor for an array of ailments and diseases (Dougall & Baum, 2001).
In addition, chronic stress has also been suggested to negatively affect structures in the
brain over time and lead to an increased risk for cognitive impairment (Sapolsky, 1996;
2000; Busciglio et al., 1998).
Individuals, who shed stress more efficiently and effectively, may be protected
against the negative effects of stress on cognitive health. It was hypothesized that
optimism would be protective against cognitive aging, such that higher optimism would
be associated with higher cognitive performance and slower rates of cognitive decline
across advancing age.
Conscientiousness. Conscientiousness is synonymous with being reliable,
industrious, and scrupulous. In contrast, individuals with lower levels of
conscientiousness are often more concerned with instant gratification than working hard
towards a goal and may be less consistent in applying moral principles (Costa & McCrae,
1992). Conscientiousness was selected because the features of this personality trait
seemed to encompass a motivation for achievement. Research has suggested that the
individuals high on conscientiousness tend to be associated with higher levels of
education and occupational attainment (Digeman, 1972; 1989; Shiner et al., 2003). In
relation to conscientiousness and cognitive performance in older adults, Baker and
Bischel (2006) found that higher conscientiousness was predictive of better auditory
processing and short-term memory in the Superior Old group, but conscientiousness did
not predict these advantages or any other advantages on cognitive performance for either
the Young or Comparable Old groups. The authors reflected that individuals higher on

11
conscientiousness may not necessarily be more intellectual, but may perform better on
cognitive tests due to their hard-working and attentive nature. Other research has
suggested that conscientiousness may be associated with higher cognitive performance on
cognitive tasks requiring sustained and complex attention (Booth et al., 2006). These
findings contradicted previous research that found a negative relationship between
conscientiousness and intelligence (Moutafi et al., 2004; Moutafi et al., 2005). Based on
these findings, it was hypothesized that due to their industrious nature, individuals high
on conscientiousness would perform better across all cognitive tasks but would not
exhibit any advantage in rate of change over advancing age.
Agreeableness. Agreeableness is described as being unselfish, cooperative, and
sympathetic to others. In contrast, disagreeable persons are competitive, egocentric, and
skeptical of others’ intentions (Costa & McCrae, 1992). Agreeableness was selected
because it seemed likely that agreeable individuals might be more socially integrated and
higher levels of social integration have been associated with a reduced risk for cognitive
decline (Fratiglioni et al. 2006). In general, research has not found agreeableness to
positively influence cognitive performance. Baker and Bischel (2006) found that higher
agreeableness was predictive of poorer cognitive performance in the Superior Old group.
Agreeableness was not predictive of cognitive performance in either the Young or
Comparable Old groups. The authors suggest that perhaps a disagreeable and competitive
nature is a feature of older individuals with more extensive general knowledge and
superior vocabulary. Research on a sample of young adults has suggested a negative
relationship between agreeableness and intelligence (Allik & Realo, 1997). In contrast,

12
Booth et al. (2006) found no relationship between agreeableness and cognitive tasks
associated with attention, orientation, memory, or executive functioning. Because
previous research has demonstrated either no or a negative relationship between
agreeableness and cognitive performance, the present study hypothesized that individuals
who were higher on agreeableness would be at no greater advantage than individuals
lower on agreeableness.
Latent Growth Models
Recent advances in statistical techniques have supplied researchers with new
methods to examine change longitudinally and provided ways to explore both
fundamental and novel issues in cognitive aging. The present study employed latent
growth curve models to measure change in cognitive performance over time and to
explore what proportion of that change could be attributed to specific personality traits.
Two factors or more can be defined based on longitudinal data across four or
more time points: an intercept, the estimate of the typical score at a specific age or point
in time, and a slope, the systematic longitudinal variation around the intercept. An
interaction effect between a personality trait and age (or age squared) would be indicative
of a difference in the trajectory of a cognitive task (slope) due to differences in level of a
personality trait. If there is reason to consider nonlinerarity, a quadratic term could be
defined to further characterize a trajectory. In such a case, longitudinal variation around
the intercept would be due to a linear slope defined at the point of the intercept plus
acceleration in the curve over age. Latent growth curve models measure and allow for
comparisons of individual trajectories of decline as well as an average trajectory of

13
decline across the entire sample. Furthermore, this technique allows for the use of both
missing and non-sequential data points and data from individuals with only one
measurement occasion can be included in the analysis to stabilize both mean and variance
estimates (Finkel, Reynolds, McArdle, Gatz, & Pedersen, 2003; McArdle & Anderson,
1990; McArdle & Hamagami, 1992). Interpretations can be formulated based on group
differences between level of personality trait (e.g. 1 SD above or below the mean). In
addition, models can be expanded to investigate and control for the effects of covariates,
such as education (Charles, Reynolds, & Gatz, 2001).
Hypotheses
In summary, it seems plausible that certain personality traits may confer qualities
that help protect against cognitive decline. While findings from the health literature
suggest that certain positive personality traits are protective of physical health; it remains
unclear whether positive personality traits are protective against declines in cognitive
health. The purpose of this study was twofold: 1.) To determine whether the specific
personality traits of openness to experience, optimism, conscientiousness, or
agreeableness were associated with cognitive performance, and 2.) to determine whether
these traits were associated with variation in the trajectories of longitudinal cognitive
change. Cognitive tests, collected lognitituindally, included Block Design, Information,
Digit Span, Thurstone’s Picture Memory, and Symobl Digit.
It was hypothesized that individuals endorsing higher levels of openness,
optimism, and conscientiousness would have higher cognitive performances across tasks
(main effect on the intercept). Higher agreeableness was not expected to result in an

14
advantage on cognitive performance. Higher openness and optimism were hypothesized
to be associated with a slower cognitive decline trajectory (interaction effect on the
slope). Trajectories were not expected to vary by level of conscientiousness or
agreeableness. In this study, four of the five cognitive tasks, including Block Design,
Digit Span, Symbol Digit and Thurstone’s Picture Memory were measures of fluid
abilities, whereas the Information task tapped crystallized abilities. These tasks were
chosen because fluid abilities have been found to be more susceptible to cognitive aging
than crystallized abilities (e.g. learned information) over time (Finkel, Reynolds,
McArdle, & Pedersen, 2005; Lindenberger, 2001). Thus, for fluid abilities, it was thought
that personality would have a greater impact on the trajectory of performance over time
than on the average performance level. In contrast, it was predicted that personality
would have a greater impact on the level of performance on the Information task than the
trajectory over time.
Chapter 3: Research Method
Participants
The sample was comprised of individuals from the Swedish Twin/ Adoption
Study of Aging (SATSA). SATSA, an on-going study, began data collection in 1984 and
collected data longitudinally every 3 years. Participants were 857 individuals (59%
female) who had both personality data and at least one cognitive measurement. The
SATSA sample was selected because it offers a large, unique source of longitudinal data
and it has been found to be representative of the larger Swedish population on a variety of
environmental and sociological variables (Cederlof, Friberg, & Lundman, 1977). It is

15
important to note that the current study treated twins as individuals and neither genetic
nor family components were incorporated into the analysis. However, as twins are not
independent of each other, correlation between twins were accounted for in the analyses.
The first questionnaire (Q1) was sent out in 1984. Q1 contained sections
regarding health, personality, rearing environment, working environment, and current
environment. Q2 was sent out in 1987, Q3 was sent in 1990, and Q4 in 1993. Because, a
portion of individuals entered the study after Q1, their personality inventories were
extracted from the first Q they completed prior to the in-person-testing session.
The in-person testing (IPT) involved three parts: an interview, the administration
of cognitive tests, and a health examination. To be included in the IPT assessments, a
twin pair had to have both responded to Q1 and be above 50 years of age. The first wave
of IPT was conducted between 1986 and 1988 (N=645). All individuals participating in
IPT1 testing were contacted for IPT2 testing regardless of the survival status of their twin
(N=595). In addition, a subsample of pairs responding to Q1 between 1986 and 1988 who
turned 50 between 1986 and 1990 were also contacted for IPT2 testing. This same pattern
was followed for the IPT3 conducted between 1992 and 1994 (N=569). IPT4, due to a
gap in funding, became a telephone interview based on a brief cognitive screening test
between 1995 and 1997 and was not included in the present analysis. All individuals who
had participated in any IPT were contacted for IPT5 regardless of their twin partner’s
status, as well as pairs who responded to Q1 who turned 50 between 1993 and 1999
(N=545).. IPT5 testing was conducted between 1999 and 2001. This same pattern was

16
follwed for IPT6 which was conducted between 2002 and 2004. (For a complete
description of the SATSA study, see Pedersen 1991.)
Measures
Personality. Personality measures for openness to experience, optimism,
conscientiousness, and agreeableness were taken from the first Q the participant
completed. Openness, conscientiousness, and agreeableness were measured by the widely
used and validated NEO-PI (Costa & McCrae, 1985). The conscientiousness and
agreeableness scales were composed of 10 items. Openness was assessed by a shortened,
six-item scale (see Bergeman et al., 1993). All three measures were scored in the
traditional fashion of the NEO based on a 5-point likert scale ranging from strongly
disagree to strongly agree. Items on each measure were summed to create a total score.
Optimism was measured via a shortened version of the Life Orientation Test (LOT;
Scheier & Carver, 1985). This measure contains four optimism and four pessimism
questions. This scale is scored based on a Yes/No response option. The four optimism
items were summed for a total score. See Appendix A.
The present study used only one time of measurement for personality scores. In
general, the stability of personality has been demonstrated repeatedly in both cross-
sectional and longitudinal studies (Costa & McCrae, 1994; Kogan 1990; Terracciano,
Costa, & McCrae, 2006). A previous study, also using SATSA data, examined openness,
extraversion, and neuroticism longitudinally in the second half of the life-span and
demonstrated mean stability of these traits across advancing age (see Pedersen &
Reynolds, 1998). In the present study, correlations between baseline personality traits and

17
cognitive scores were found to decrease across time for some trait-cognitive
combinations but remained relatively stable for others (Table 1).

18
Table 1.
Correlations between personality traits and cognitive tasks across measurement occasions by sex.

*p<.05, **p<.001, ***p<.0001

Cognitive
Openness Optimism Conscientiousness Agreeableness
Task Females Males Females Males Females Males Females Males
Block Design
IPT1 0.18** 0.38*** -0.03 -0.16* 0.00 -0.11 0.02 -0.20*
IPT2 0.27*** 0.34*** -0.11* -0.11 0.06 -0.07 0.00 -0.15*
IPT3 0.14* 0.36*** -0.14* 0.01 -0.07 -0.10 -0.03 -0.12
IPT5 0.26*** 0.40*** -0.01 0.07 0.06 -0.00 -0.11 -0.01
IPT6 0.09 0.38*** -0.01 0.08 0.02 0.14 -0.03 -0.08
Information
IPT1 0.27*** 0.34*** -0.11* -0.13 -0.09 -0.13 -0.04 -0.16*
IPT2 0.32*** 0.26*** -0.18* -0.09 -0.09 -0.20* -0.03 -0.09
IPT3 0.25*** 0.32*** -0.21*** -0.05 -0.11 -0.06 -0.12* -0.12
IPT5 0.22*** 0.43*** -0.12* -0.01 -0.06 -0.13 -0.08 -0.14
IPT6 0.24*** 0.38*** -0.13* 0.00 0.01 -0.11 -0.07 -0.03
Digit Span
IPT1 0.18** 0.27*** -0.02 -0.05 -0.08 -0.02 -0.06 -0.01
IPT2 0.15* 0.17* -0.06 -0.04 0.00 -0.13 -0.07 -0.06
IPT3 0.15* 0.28*** -0.12* -0.01 -0.08 -0.07 -0.15* -0.01
IPT5 0.15* 0.27*** -0.01 0.04 -0.08 -0.11 -0.09 0.08
IPT6 0.08 0.20* 0.04 0.09 -0.11 0.01 -0.04 0.12

19
Table 1. (continued)

Cognitive
Openness Optimism Conscientiousness Agreeableness
Task Females Males Females Males Females Males Females Males
Thurstone’s

IPT1 0.14* 0.34*** -0.01 -0.04 -0.08 0.04 0.01 -0.06
IPT2 0.24*** 0.25*** -0.08 0.00 -0.01 -0.03 -0.06 -0.07
IPT3 0.17* 0.33*** -0.08 -0.06 0.01 -0.08 -0.06 -0.10
IPT5 0.20** 0.46*** -0.03 -0.02 0.03 -0.07 -0.02 -0.05
IPT6 0.16* 0.28** 0.03 -0.01 0.02 0.04 -0.13 0.12
Symbol Digit

IPT1 0.20*** 0.44*** -0.13* -0.04 -0.04 -0.07 -0.05 -0.17*
IPT2 0.19** 0.40*** -0.20** -0.09 0.01 -0.09 -0.11 -0.14*
IPT3 0.17* 0.38*** -0.24*** 0.05 -0.02 0.08 -0.11 -0.13
IPT5 0.17* 0.47*** -0.11 0.01 -0.00 -0.01 -0.10 -0.10
IPT6 0.15* 0.37*** -0.06 0.08 -0.05 0.09 -0.09 -0.02

*p<.05, **p<.001, ***p<.0001

20
Cognition. The original IPT cognitive battery included 13 cognitive measures
designed to assess fluid and crystallized abilities. Of the 13 tests, 5 were selected for this
study. Fluid ability was assessed via Koh’s Block Design (Arthur, 1974); Digit Span
(CVB [Central Varnpliktsbyran] or Swedish WAIS scales; Jonasson & Molander, 1964);
Thurstone’s Picture Memory (Thurstone, 1938); and Symbol Digit (Smith, 1982).
Crystallized ability was examined via Information (CVB [Central Varnpliktsbyran] or
Swedish WAIS scales; Jonsson & Molander, 1964). Reliabilities of these measures
ranged from .82 to .92 (Pedersen et al., 1992). For the data analyses, test scores were
converted to percentage correct for each cognitive measure. Test descriptions are
provided below:
Koh’s Block Design. A test of spatial ability to determine a participant’s skill at
assembling blocks to match seven different and increasingly difficult patterns. More
points were awarded for faster completion of each block design. The maximum score was
42.
Digit Span. Digit span was calculated as the combination of the highest number of
digits forward and digits backward the participant was able to repeat correctly. The
maximum score was 16.
Thurstone’s Picture Memory. This task calls on recognition memory of drawings
of common items (e.g. truck, table). Twenty-eight target drawings were presented for five
seconds each. Participants were asked to identify the drawings on a 28-item four-choice
recognition task. The maximum score was thus 28.

21
Symbol Digit. A task of processing speed similar to the standard WAIS Digit
Symbol, except that participants verbally report the numbers that correspond to the
symbols. The advantage of this presentation was that it is less affected by motor
limitations of the participant. The maximum score over two halves of the test was 100.
Information. A shortened version of the Swedish Wechsler Adult Intelligence
Scale [WAIS] Information test. It contained 11 items scored as 0, 1, or 2. The maximum
score was 22.
Covariates. The main covariate for this study was education. Several studies have
demonstrated that low educational attainment is predicative of an increased risk of
dementia (Albert et al., 1995; Christiansen et al., 1999; Gatz et al., 2001; Leibovici et al.,
1996). Educational attainment was treated as a continuous variable ranging from 1
(elementary school) to 4 (university or higher).
Two additional covariates were explored in the analyses. Recent research has
suggested that vascular risk factors may contribute to an increased risk for Alzheimer’s
disease (Breteler, 2000; Vermeer et al., 2003). In particular, a review of the literature
demonstrated that both hypertension and cardiovascular disease were associated with an
increased risk for cognitive decline (Anstey & Christensen, 2000). In relation to the
current study, there was concern over a potential relationship between personality and
vascular health. Thus, data regarding cardiovascular disease (CVD) were extracted from
the SATSA questionnaires. CVD was measured via a 13-item yes-no scale regarding the
presence of cardiovascular disorders. If any one item or combination of items was

22
endorsed, and if that response met criteria as an indicator of cardiovascular disease, CVD
was coded as present.
Activities of Daily Living (ADL) was identified as a potential control variable due
to a possible relationship between disability and personality scores. ADL was measured
via a 14-item yes-no scale. Seven questions pertained to instrumental activities and seven
questions pertained to physical activities. A total score was summed across questions. See
Appendix B for ADL and CVD scales.
Chapter 4: Statistical Method
Latent growth curve models were employed to investigate the pattern of change in
cognition across advancing age and whether differences in cognitive ability were
associated with specific personality traits. This type of model can also be considered a
random coefficients model (Bryk & Raudenbush, 1987), wherein individual regression
models are fitted to each participant’s profile of longitudinal data, as well as, an average
model of growth estimated over the entire sample. Latent growth curve models allow for
missing data by giving more weight to individuals with the most measurement occasions,
or time points.
The role of personality in cognitive change was investigated by expanding an
existing phenotypic latent growth model (McArdle, Ferrer-Caja, Hamagami, &
Woodcock, 2002; McArdle & Nesselroade, 2003). An example of a linear latent growth
model, expanded to include a covariate (e.g. personality) and a control variable (e.g.
education), is presented in Figure 1. Longitudinal change was defined by chronological
age (and age-squared) rather than by time or measurement occasion (as specified by

23
McArdle et al., 1998). Both Linear and quadratic models were considered for all traits
except Digit Span because prior analyses of the Digit Span data had suggested
nonlinearity (Reynolds et al. 2005). Because this sample was comprised of individuals
who were twins, and twins are not independent of each other, models were adjusted to
account for the correlation between twins.
Age, education, ADL, CVD, and personality traits were centered on their mean.
Prior to conducting growth curve analysis, a series of descriptive analyses were
undertaken. Correlation matrices were fit for each personality trait by cognitive measure
by IPT session. Correlation matrices were also fit for personality traits and sex,
education, ADL, and CVD. ADL and CVD were explored in the descriptive portion of
the analyses and then dropped from further analyses because neither was correlated with
the personality traits of interest. Males and females were found to differ on study
constructs including, personality traits, cognitive measures, and education. Because of
these differences, males and females were modeled separately.
Using PROC MIXED (SAS Institute 9.0, 2000), latent growth modeling was used
to conduct the analyses. For each personality trait, a stepwise procedure was adopted to
evaluate longitudinal trajectories. Initial growth curve analyses established linear or
nonlinear age trends for all cognitive tasks prior to including personality traits in the
analyses. Mean centered education was then added to the model as a control variable.
Next, the personality variable of interest was added to the model. Lastly, interaction
terms for linear and nonlinear age with personality covariate (predictor variable), were
added to the model.

24

Figure 1. Latent Growth Curve Model

Typical of many representations of structural equation models, the squares represent
observed, or measured, variables, whereas the circles denote latent variables; single-headed
arrows represent regression coefficients, and double-headed arrows denote covariation. The
triangle, though less customary, represents a unit constant that allows for the estimation of means;
the circles within squares represent data that are available for an individual participant at some
but not necessarily all time points.
r
cso
= correlation between the slope and the covariate (openness); r
cse
= correlation
between the slope and the control variable (education) M
co
= mean of the covariate Openness; M
ce

= mean of the control variable education; M
i
= mean of the intercept; M
s
= mean of the slope; r
ci
=
correlation between the covariate and the intercept; r
is
= correlation between the slope and the
intercept; Openness* = standardized score of the covariate; Education* = standardized score of
the control variable; I* = standardized score for the intercept; S* = standardized score for the
slope; D
co
=deviation from the covariate mean; D
ce
= deviation from the control variable mean; D
i

= deviation from the intercept; D
s
= deviation from the slope; I = intercept; S = slope; B1-B4 =
age basis coefficients; y
0
-y
4
= cognition scores at each time point; u
0
-u
4
= random components
from the cognition scores; D
u
= the constant deviation from the cognition scores. (Adapted from
Charles, Reynolds, & Gatz, 2001).

25
A frequent concern of longitudinal studies is missing data and whether the
patterns of missing data are ignorable or nonignorable. Previous research, using the
SATSA data, examined cognitive scores and established that dropout (due to death or
refusal) did not explain the decline in cognitive scores over time (Dominicus, Palmgren,
& Pedersen, 2005). This suggests that patterns of missingness in this longitudinal study
may be ignorable. Based on this previous research, a full maximum-likelihood estimate
(MLE) technique was used in the growth models. This technique aggregates all available
data on any participant included in the analyses to estimate the model parameters. A basic
statistical assumption of MLE is that the incomplete data points are missing at random
(MAR). In this study, since missingness was assumed to be ignorable, MAR was
applied. The MAR assumption is typically applied to incomplete longitudinal data (Little,
1995; McArdle et al., 2004).
It is important to note that the SATSA data included individuals who were
eventually diagnosed with dementia. Because both personality scores and, in particular,
cognitive trajectories could be very different for those who became demented, models
were fit for two datasets. One removed all individuals identified as ever meeting criteria
for a dementia diagnosis (N=62) and the other included these individuals. Overall results
did not differ between the two groups. Therefore, results reported here reflect a
population of both nondemented individuals and individuals who at some time during
longitudinal follow-up were diagnosed as demented.

26
Chapter 5: Results
Mean age and sample size by personality trait across measurement
occasions is listed in Table 2. Descriptive statistics by sex for openness, optimism,
conscientiousness, and agreeableness, measured at each individual’s baseline, are listed
in Table 3. Means and standard deviations for the cognitive measures across
measurement occasions by sex can be found in Table 4. Correlation of personality with
education, ADL, and CVD, by sex is shown in Table 5. Neither ADL nor CVD was
correlated with any personality trait and so were not included as control variables in the
analyses. As predicted, openness was positively correlated with education for both males
and females.
The number of individuals with only one time point of measurement through all
five measurement points for cognitive data is listed in Table 6. A crosstabulation of these
measurement points is shown in Table 7. Correlations of personality traits and cognitive
tasks are presented in Table 1. Openness was significantly positively correlated with
nearly all measurement occasions of each cognitive task for both males and females.
Graphical illustrations of performance trajectories across advancing age of a random
sample of males and females on Block Design, Information, Digit Span, Thurstone’s
Picture Memory, and Symbol Digit are presented in Figures 2– 6.

27
Table 2.
Ns and ages of participants who had at least one cognitive measurement, shown for each wave of cognitive
data by each personality scale.

Time of Measurement
Statistic
IPT1 IPT2 IPT3 IPT5 IPT6
Openness to Experience
n 597 568 557 528 432
Mean age 66.2 (7.5) 66.4 (8.6) 68.7 (9.0) 70.61 (9.93) 72.30 (9.21)
Age range 50 – 88 50 – 91 50 – 94 51 – 96 54 – 95
Optimism
n 587 567 559 528 433
Mean age 66.2 (7.5) 66.4 (8.6) 68.8 (9.1) 70.65 (9.99) 72.27 (9.22)
Age range 50 – 88 50 – 91 50 – 94 51 – 96 54 – 95
Conscientiousness
n 514 490 479 452 380
Mean age 65.8 (7.3) 66.0 (8.5) 68.2 (9.0) 70.7 (9.5) 72.6 (8.9)
Age range 50 – 88 50 – 91 50 – 94 51 – 93 54 – 95
Agreeableness
n 524 493 482 448 378
Mean age 66.0 (7.4) 66.2 (8.5) 68.4 (9.1) 70.7 (9.5) 72.7 (8.89)
Age range 50 – 88 50 – 91 50 – 94 51 – 93 54 – 95

Table 3.
Means, standard deviations and range for personality traits by sex.

Personality Trait Mean Stand. Dev. Range

Openness to Experience
All 17.78 4.12 6-30
Men 17.67 3.93 6-28
Women 17.85 4.26 6-30
Optimism
All 15.31 2.36 6-20
Men 15.16 2.19 8-20
Women 15.41 2.47 6-20
Conscientiousness
All 37.90 4.41 22-49
Men 37.64 4.21 23-49
Women 38.09 4.55 22-48
Agreeableness
All 38.78 3.96 24-50
Men 37.46 3.73 24-50
Women 39.74 3.85 27-50

28
Table 4.
Means and Standard Deviations for Cognitive Measures at Five Times of Measurement by Sex, with Cognitive Measures Scored for Percent
Correct

Time of Measurement

Cognitive
Measure
IPT1 IPT2 IPT3 IPT5 IPT6

Block Design
Females 41.8 (17.7) 44.2 (17.0) 43.8 (18.7) 46.3 (17.7) 45.0 (18.4)
Males 46.0 (18.9) 46.3 (16.3) 46.3 (18.6) 49.3 (18.9) 48.2 (18.9)
Information
Females 65.7 (18.6) 68.2 (18.3) 67.7 (18.2) 68.3 (20.2) 73.3 (18.8)
Males 76.9 (18.1) 77.0 (16.1) 78.3 (15.8) 78.9 (17.4) 81.3 (15.8)
Digit Span
Females 56.3 (12.5) 58.0 (12.6) 57.1 (13.2) 55.0 (13.0) 56.2 (13.5)
Males 57.5 (12.8) 59.0 (12.4) 58.4 (14.0) 56.5 (12.6) 56.3 (13.2)
Thurstone’s
Females 75.0 (16.2) 75.7 (16.2) 78.4 (15.8) 76.7 (17.6) 77.8 (15.9)
Males 70.5 (16.6) 72.0 (16.9) 73.4 (19.1) 75.0 (16.9) 75.4 (16.3)
Symbol Digit
Females 37.6 (11.8) 37.5 (11.6) 37.9 (13.0) 35.7 (12.5) 36.4 (12.0)
Males 38.3 (12.1) 38.1 (11.7) 38.2 (13.2) 36.6 (12.4) 35.6 (12.9)

29
Table 5.
Correlations between personality traits and covariates by sex.

Covariate Education ADL CVD
Females Males Females Males Females Males

Education 1.00 1.00
ADL 0.07 0.06 1.00 1.00
CVD -0.08 -0.13* -0.20*** -0.01 1.00 1.00
Agreeableness -0.08 -0.10 0.03 0.06 -0.02 -0.05
Conscientiousness -0.03 0.01 -0.06 -0.01 0.04 0.02
Openness 0.24*** 0.33*** 0.06 0.07 -0.04 -0.04
Optimism -0.06 -0.05 0.02 0.06 0.08 0.02
*p<.01, **p<.001, *** p<.0001

30
Table 6.
Number of individuals with cognitive measurements from 1 time point to all 5 time points.

Number of
measurement points
N Percent
1 113

13.3%
2 178 20.9%
3 199 23.4%
4 143 16.8%
5 217 25.8%

Table 7.
Crosstabulation of available cognitive data for individuals from each IPT measurement occasion.
For example, 618 individuals had cognitive data for IPT1 and 480 individuals had cognitive data
for both IPT1 and IPT2.

Measurement
occasion
IPT1 IPT2 IPT3 IPT5 IPT6

IPT1 618
IPT2 480 576
IPT3 449 506 567
IPT5 373 373 399 541
IPT6 294 294 315 430 442

31
Figure 2a.
A random sample of trajectories on Block Design for Females.

Figure 2b.
A random sample of trajectories on Block Design for Males.

32
Figure 3a.
A random sample of trajectories on Information for Females

Figure 3b.
A random sample of trajectories on Information for Males

33
Figure 4a.
A random sample of trajectories on Digit Span for Females.

Figure 4b.
A random sample of trajectories on Digit Span for Males.

34
Figure 5a.
A random sample of trajectories on Thurstone’s Picture Memory for Females.

Figure 5b.
A random sample of trajectories on Thurstone’s Picture Memory for Males.

35
Figure 6a.
A random sample of trajectories on Symbol Digit for Females.

Figure 6b.
A random sample of trajectories on Symbol Digit for Males.

36
Table 8.
Females: Relation of personality traits to change in cognitive functioning as measured by the Block Design task, controlling for education.

Outcome Trait Model Term Estimate (SE) p value

Block Design Openness Age -0.425 (0.050) <0.0001
(Spatial) Age squared -0.044 (0.007) <0.0001
Openness 0.630 (0.171) 0.0002
Openness x Age 0.002 (0.011) 0.878
Openness x Age squared -0.004 (0.001) 0.007
Optimism Age -0.415 (0.045) <0.0001
Age squared -0.045 (0.007) <0.0001
Optimism -0.097 (0.285) 0.733
Optimism x Age -0.037 (0.019) 0.058
Optimism x Age squared 0.002 (0.003) 0.375
Conscientiousness Age -0.435 (0.051) <0.0001
Age squared -0.046 (0.007) <0.0001
Conscientiousness 0.043 (0.162) 0.789
Conscientiousness x Age -0.006 (0.010) 0.546
Conscientiousness x Age squared -0.002 (0.002) 0.258
Agreeableness Age -0.426 (0.045) <0.0001
Age squared -0.042 (0.006) <0.0001
Agreeableness 0.126 (0.191) 0.511
Agreeableness x Age -0.007 (0.115) 0.596
Agreeableness x Age squared -0.002 (0.002) 0.193

37
Table 9.
Females: Relation of personality traits to change in cognitive functioning as measured by the Information task, controlling for education.

Outcome Trait Model Term Estimate (SE) p value

Information Openness Age 0.133 (0.054) 0.036
(Verbal) Age squared -0.071 (0.008) <0.0001
Openness 0.835 (0.174) <0.0001
Openness x Age -0.003 (0.011) 0.808
Openness x Age squared 0.000 (0.002) 0.961
Optimism Age 0.130 (0.053) 0.014
Age squared -0.071 (0.008) <0.0001
Optimism -0191 (0.294) 0.516
Optimism x Age -0.020 (0.020) 0.296
Optimism x Age squared -0.003 (0.003) 0.315
Conscientiousness Age 0.080 (0.053) 0.135
Age squared -0.069 (0.008) <0.0001
Conscientiousness -0.225 (0.161) 0.161
Conscientiousness x Age 0.007 (0.010) 0.512
Conscientiousness x Age squared 0.001 (0.002) 0.683
Agreeableness Age 0.074 (0.054) 0.167
Age squared -0.068 (0.008) <0.0001
Agreeableness 0.024 (0.188) 0.899
Agreeableness x Age -0.001 (0.013) 0.888
Agreeableness x Age squared -0.001 (0.001) 0.619

38
Table 10.
Females: Relation of personality traits to change in cognitive functioning as measured by the Digit Span task, controlling for education.

Outcome Trait Model Term Estimate (SE) p value

Digit Span Openness Age -0.315 (0.038) <0.0001
(Memory) Openness 0.250 (0.121) 0.038
Openness x Age 0.001 (0.008) 0.951
Optimism Age -0.314 (0.038) <0.0001
Optimism -0.092 (0.201) 0.646
Optimism x Age 0.003 (0.014) 0.826
Conscientiousness Age -0.342 (0.041) <0.0001
Conscientiousness -0.138 (0.110) 0.212
Conscientiousness x Age -0.008 (0.008) 0.316
Agreeableness Age -0.331 (0.042) <0.0001
Agreeableness -0.044 (0.130) 0.737
Agreeableness x Age -0.003 (0.010) 0.753

39
Table 11.
Females: Relation of personality traits to change in cognitive functioning as measured by the Thurstone’s Picture Memory task, controlling for
education.

Outcome Trait Model Term Estimate (SE) p value

Thurstone’s Openness Age -0.189 (0.058) <0.0001
(Memory) Age squared -0.050 (0.009) 0.001
Openness 0.404 (0.169) 0.017
Openness x Age -0.020 (0.012) 0.111
Openness x Age squared 0.004 (0.002) 0.046
Optimism Age -0.209 (0.058) <0.0001
Age squared -0.049 (0.009) 0.0004
Optimism 0.345 (0.275) 0.209
Optimism x Age -0.046 (0.023) 0.045
Optimism x Age squared 0.000 (0.003) 0.836
Conscientiousness Age -0.261 (0.056) <0.0001
Age squared -0.040 (0.009) <0.0001
Conscientiousness -0.263 (0.152) 0.084
Conscientiousness x Age 0.001 (0.011) 0.914
Conscientiousness x Age squared 0.002 (0.002) 0.296
Agreeableness Age -0.259 (0.057) <0.0001
Age squared -0.036 (0.009) <0.0001
Agreeableness 0.125 (0.183) 0.494
Agreeableness x Age -0.005 (0.014) 0.699
Agreeableness x Age squared -0.002 (0.002) 0.396

40
Table 12.
Females: Relation of personality traits to change in cognitive functioning as measured by the Symbol Digit task, controlling for education.

Outcome Trait Model Term Estimate (SE) p value

Symbol Digit Openness Age -0.706 (0.037) <0.0001
(Proc. Speed) Age squared -0.017 (0.005) <0.0001
Openness 0.341 (0.104) 0.001
Openness x Age 0.010 (0.007) 0.171
Openness x Age squared 0.001 (0.001) 0.351
Optimism Age -0.695 (0.036) <0.0001
Age squared -0.019 (0.005) <0.0001
Optimism -0.221 (0.172) 0.198
Optimism x Age 0.012 (0.013) 0.364
Optimism x Age squared -0.001 (0.002) 0.444
Conscientiousness Age -0.670 (0.037) <0.0001
Age squared -0.019 (0.005) <0.0001
Conscientiousness -0.073 (0.099) 0.458
Conscientiousness x Age -0.018 (0.007) 0.008
Conscientiousness x Age squared 0.002 (0.001) 0.094
Agreeableness Age -0.698 (0.037) <0.0001
Age squared -0.018 (0.005) 0.0005
Agreeableness -0.011 (0.118) 0.924
Agreeableness x Age -0.002 (0.008) 0.729
Agreeableness x Age squared 0.000 (0.001) 0.840

41
Latent growth models were fit for each cognitive task by personality trait by age
and age- squared. Education was controlled for within each model. Interactions between
age and personality trait reflect differences in the trajectory of cognitive performance
across advancing age. Models were fit for males and females separately and are described
separately below. Model results are summarized in Tables 8-17.
Females
Results for latent growth curve models for females are summarized in Tables 8 –
12. Significant average performance effects (intercept) were found for openness to
experience across all cognitive tasks while controlling for education. Females who
endorsed higher levels of openness (1 SD above the mean) performed significantly better
on Block Design (p=0.005), Information (p<0.0001), Digit Span (p=0.03), Thurstone’s
Picture Memory (p<0.0001), and Symbol Digit (p=0.0004) at the centering age of 65
(See Figure 7).
In terms of trajectories, females endorsing higher levels of openness were
associated with a slower rate of decline on the Thurstone’s Picture Memory task
(p=0.05). See Figure 8. Females endorsing higher levels of openness indicated a faster
rate of decline in cognitive performance on Block Design than females low on openness
(p=0.01). Despite this faster decline, a higher average performance was maintained across
time for those individuals endorsing higher openness (See Figure 9).

42
Figure 7.
Main effects of Openness to Experience across each cognitive task over three age intervals (55,
65, and 75) for females, controlling for education.

0
10
20
30
40
50
60
70
80
90
55 65 75 55 65 75 55 65 75 55 65 75 55 65 75
Blck Dsgn Information Digit Span Thurstone's Sybl Digit
Cognitive Test by Age
Percentage Correct
Openness +1sd
Openness -1sd

Figure 8.
Females who endorsed higher levels of Openness performed better on the Thurstone’s Picture
Memory task before age 65 and had slower rates of decline.

25.00
35.00
45.00
55.00
65.00
75.00
85.00
50 55 60 65 70 75 80
Age
Percent Correct
Openness + 1SD
Openness - 1SD

43
Figure 9.
Females who endorsed higher levels of Openness to Experience on Block Design were at an
advantage for level of performance, but had faster rates of decline.

20
30
40
50
60
70
80
50 55 60 65 70 75 80
Age
Percentage Correct
Openness + 1SD
Openness - 1SD

No effects on average performance (intercept) were found for optimism,
conscientiousness, or agreeableness. In terms of trajectories, results indicated significant
differences in slope between levels of optimism on Thurstone’s Picture Memory and
between levels of conscientiousness on Symbol Digit. Higher levels of optimism and
conscientiousness were predictive of a greater advantage in performance before age 65
but a faster trajectory of decline after age 65 on Thurstone’s Picture Memory and Symbol
Digit, respectively (See Figures 10 and 11). No differences in the trajectories of cognitive
performance (slope) were related to level of agreeableness.

44
Figure 10.
Females who endorsed higher levels of Optimism initially performed better on the Thurstone’s
Picture Memory task before age 65 but had faster rates of decline.

20
30
40
50
60
70
80
50 55 60 65 70 75 80
Age
Percent Correct
Opti + 1SD
Opti - 1SD

Figure 11.
Females who endorsed higher levels of Conscientiousness had an advantage on the Symbol Digit
task before age 65 had a faster rate of decline.

20
30
40
50
60
70
80
50 55 60 65 70 75 80
Age
Percentage Correct
Consci + 1SD
Consci - 1SD

45
Table 13.
Males: Relation of personality traits to change in cognitive functioning as measured by the Block Design task, controlling for education.

Outcome Trait Model Term Estimate (SE) p value

Block Design Openness Age -0.538 (0.057) <0.0001
(Spatial) Age squared -0.037 (0.009) <0.0001
Openness 0.835 (0.214) <0.0001
Openness x Age 0.007 (0.014) 0.559
Openness x Age squared 0.000 (0.002) 0.883
Optimism Age -0.527 (0.052) <0.0001
Age squared -0.033 (0.008) 0.000
Optimism -0.709 (0.334) 0.034
Optimism x Age 0.032 (0.021) 0.132
Optimism x Age squared 0.006 (0.003) 0.061
Conscientiousness Age -0.559 (0.054) <0.0001
Age squared -0.039 (0.009) <0.0001
Conscientiousness -0.477 (0.195) 0.015
Conscientiousness x Age 0.013 (0.012) 0.277
Conscientiousness x Age squared 0.000 (0.002) 0.912
Agreeableness Age -0.553 (0.057) <0.0001
Age squared -0.039 (0.009) <0.0001
Agreeableness -0.302 (0.214) 0.158
Agreeableness x Age -0.007 (0.014) 0.620
Agreeableness x Age squared 0.001 (0.002) 0.727

46
Table 14.
Males: Relation of personality traits to change in cognitive functioning as measured by the Information task, controlling for education.

Outcome Trait Model Term Estimate (SE) p value

Information Openness Age 0.056 (0.052) 0.277
(Verbal) Age squared -0.047 (0.008) <0.0001
Openness 0.654 (0.184) 0.0004
Openness x Age 0.005 (0.012) 0.645
Openness x Age squared 0.001 (0.002) 0.685
Optimism Age 0.054 (0.051) 0.298
Age squared -0.044 (0.008) <0.0001
Optimism -0.792 (0.310) 0.011
Optimism x Age -0.020 (0.021) 0.343
Optimism x Age squared 0.007 (0.003) 0.032
Conscientiousness Age 0.026 (0.050) <0.609
Age squared -0.045 (0.008) <0.0001
Conscientiousness -0.742 (0.171) <0.0001
Conscientiousness x Age 0.024 (0.011) 0.037
Conscientiousness x Age squared 0.000 (0.002) 0.929
Agreeableness Age 0.016 (0.054) 0.764
Age squared -0.044 (0.009) <0.0001
Agreeableness -0.384 (0.194) 0.049
Agreeableness x Age -0.011 (0.013) 0.397
Agreeableness x Age squared 0.003 (0.002) 0.236

47
Table 15.
Males: Relation of personality traits to change in cognitive functioning as measured by the Digit Span task, controlling for education.

Outcome Trait Model Term Estimate (SE) p value

Digit Span Openness Age -0.362 (0.047) <0.0001
(Memory) Openness 0.430 (0.152) 0.005
Openness x Age 0.001 (0.011) 0.909
Optimism Age -0.372 (0.047) <0.0001
Optimism -0.047 (0.258) 0.858
Optimism x Age 0.008 (0.020) 0.704
Conscientiousness Age -0.377 (0.049) <0.0001
Conscientiousness -0.221 (0.143) 0.121
Conscientiousness x Age 0.020 (0.011) 0.088
Agreeableness Age -0.374 (0.052) <0.0001
Agreeableness 0.110 (0.162) 0.499
Agreeableness x Age 0.003 (0.013) 0.792

48
Table 16.
Males: Relation of personality traits to change in cognitive functioning as measured by Thurstone’s Picture Memory task, controlling for
education.

Outcome Trait Model Term Estimate (SE) p value

Thurstone’s Openness Age -0.295 (0.060) <0.0001
(Memory) Age squared -0.016 (0.010) <0.0001
Openness 0.868 (0.209) <0.0001
Openness x Age 0.001 (0.014) 0.931
Openness x Age squared 0.002 (0.002) 0.372
Optimism Age -0.306 (0.064) <0.0001
Age squared -0.024 (0.011) 0.029
Optimism -0.257 (0.373) 0.491
Optimism x Age -0.034 (0.027) 0.208
Optimism x Age squared -0.003 (0.005) 0.517
Conscientiousness Age -0.350 (0.065) <0.0001
Age squared -0.010 (0.011) 0.346
Conscientiousness -0.139 (0.210) 0.508
Conscientiousness x Age -0.019 (0.015) 0.202
Conscientiousness x Age squared -0.005 (0.002) 0.276
Agreeableness Age -0.401 (0.063) <0.0001
Age squared -0.007 (0.012) <0.0001
Agreeableness -0.048 (0.233) 0.836
Agreeableness x Age -0.021 (0.016) 0.189
Agreeableness x Age squared -0.000 (0.003) 0.872

49
Table 17.
Males: Relation of personality traits to change in cognitive functioning as measured by the Symbol Digit task, controlling for education.

Outcome Trait Model Term Estimate (SE) p value

Symbol Digit Openness Age -0.660 (0.036) <0.0001
(Proc. Speed) Age squared -0.028 (0.005) <0.0001
Openness 0.691 (0.126) <0.0001
Openness x Age 0.014 (0.008) 0.108
Openness x Age squared -0.002 (0.001) 0.119
Optimism Age -0.668 (0.035) <0.0001
Age squared -0.027 (0.005) <0.0001
Optimism -0.219 (0.225) 0.329
Optimism x Age -0.016 (0.015) 0.283
Optimism x Age squared 0.001 (0.002) 0.718
Conscientiousness Age -0.661 (0.036) <0.0001
Age squared -0.029 (0.005) <0.0001
Conscientiousness -0.104 (0.123) 0.401
Conscientiousness x Age -0.010 (0.008) 0.228
Conscientiousness x Age squared -0.000 (0.001) 0.876
Agreeableness Age -0.719 (0.035) <0.0001
Age squared -0.025 (0.005) <0.0001
Agreeableness -0.152 (0.137) 0.267
Agreeableness x Age -0.036 (0.009) 0.0001
Agreeableness x Age squared 0.002 (0.001) 0.212

50
Males
Results for latent growth curve models for males are summarized in Tables 13 –
17. Significant average performance effects (intercept) were found for openness to
experience across all cognitive tasks while controlling for education. Males who endorsed
higher levels of Openness performed significantly better on Block Design (p<0.0001),
Information (p<0.0001), Digit Span (p=0.003), Thurstone’s Picture Memory (p<0.0001),
and Symbol Digit (p<0.0001) at the centering age of 65 (See Figure 12). Openness was
not found to be associated with rates of cognitive decline (slope).

Figure 12.
Main effects of Openness to Experience across each cognitive task over three age intervals (55,
65, and 75) for males, controlling for education.

0
10
20
30
40
50
60
70
80
90
55 65 75 55 65 75 55 65 75 55 65 75 55 65 75
Blck Dsgn Information Digit Span Thurstone's Sybl Digit
Cognitive Tasks by Age
Percentage Correct
Openness +1sd
Openness -1sd

Significant negative average performance effects (intercept) were found for
optimism and Block Design (p=0.03), conscientiousness and Block Design (p=0.01),
conscientiousness and Information (p<0.0001), optimism and Information (p=0.03), and

51
agreeableness and Information (p=.05), such that individuals who endorsed higher levels
of these traits performed poorer on these cognitive tasks at the centering age of 65 (See
Figures 13-17).

Figure 13.
Males who endorsed higher levels of Optimism performed more poorly on the Block Design task
at the centering age of 65 (main effect only).

20
30
40
50
60
70
80
50 55 60 65 70 75 80
Age
Percentage Correct
Opti + 1SD
Opti - 1SD

Figure 14.
Males who endorsed higher levels of Conscientiousness performed more poorly on the Block
Design task at the centering age of 65 (main effect only).

20
30
40
50
60
70
80
50 55 60 65 70 75 80
Age
Percentage Correct
Conscien + 1SD
Conscien - 1SD

52
Figure 15.
Males who endorsed higher levels of Conscientiousness performed more poorly on the
Information task but had slower rates of decline than individuals endorsing lower levels of
Conscientiousness.

20
30
40
50
60
70
80
50 55 60 65 70 75 80
Age
Percentage Correct
Conscien + 1SD
Conscien - 1SD

Figure 16.
Males who endorsed higher levels of Optimism performed more poorly on the Information task
but had slower rates of decline than individuals endorsing lower levels of Optimism (nonlinear
effect on slope).

25
35
45
55
65
75
85
50 55 60 65 70 75 80
Age
Percentage Correct
Opti + 1SD
Opti - 1SD

53
Figure 17.
Males who endorsed higher levels of Agreeableness performed more poorly on the Information
task at the centering age of 65 (main effect only).

30
40
50
60
70
80
90
50 55 60 65 70 75 80
Age
Percent Correct
Agree + 1SD
Agree - 1SD

Figure 18.
Males who endorsed higher levels of Agreeableness had an advantage prior to age 65 in
performance on Symbol Digit but had a faster rate of decline (linear effect on slope).

20
30
40
50
60
70
80
50 55 60 65 70 75 80
Age
Percentage Correct
Agree + 1SD
Agree - 1SD

54
In terms of trajectories, higher agreeableness was associated with a faster
trajectory of decline in cognitive performance on Symbol Digit (p=0.0003). See Figure
18. In contrast, higher conscientiousness and optimism were each associated with slower
rates of decline in cognitive performance on the Information task (p=0.04 and 0.03,
respectively), yet—as noted above—were also associated with an overall poorer
performance on these cognitive tasks. See Figures 15 and 16.
Among both males and females, as predicted, openness to experience was
predictive of a significantly better performance across all cognitive tasks even when
controlling for education. However, contrary to hypothesis, few associations were found
between openness and rates of cognitive decline, and where relationships were observed,
they were in the opposite direction from what was predicted. Although it was also
hypothesized that higher levels of conscientiousness and optimism would be associated
with better cognitive performance, this was generally not supported, and in some cases
these personality measures were found to be associated with poorer cognitive
performance. The hypothesized relationship between optimism and slower cognitive
decline received minimal support. As predicted, agreeableness did not confer an
advantage on cognitive performance or protect against cognitive decline. The expectation
that relationships between level and cognition would be stronger for crystallized than
fluid tasks while relationships between slope and cognition would be stronger for fluid
than for crystallized tasks was not born out. Indeed, men showed the greatest associations
between slope and cognition for the one test of crystallized intelligence. In general, the
effect sizes between personality and cognitive performance were small.

55
Chapter 6: Discussion
Personality has been widely studied in the field of health psychology, yet little
research has extended this line of thinking to examining the relationship between
cognitive aging and decline in older adults. This study tested whether specific personality
traits were protective of cognitive functioning and cognitive decline across advancing
age. Two possible mechanisms that might explain relationships between personality and
cognition are the cognitive-reserve hypothesis and stress-reduction. These two
mechanisms were suggested by Fratiglioni, Paillard-Borg, and Winblad’s (2004) as
potentially accounting for the link between lifestyle activities (social, mental, or physical)
and decreased risk for cognitive decline and dementia.
Openness to experience, as predicted, was most associated with cognitive
performance. Males and females who endorsed higher levels of openness performed
significantly better across all cognitive tasks and this advantage was maintained over
time. Importantly, because openness was correlated with education, the higher level of
cognitive performance for those who were higher on openness held across all cognitive
tasks even when controlling for education. These findings support previous literature on
the relationship between openness to experience and cognitive performance (Baker &
Bischel, 2006; Booth et al., 2006; Schaie et al., 2004). Openness has been associated with
a basic cognitive capacity and the enjoyment of experiencing and thinking about novel
ideas (McCrae, 1994). In relation to the successful aging, openness may lead to cognitive
resources that aid in maintaining life-long advantages in cognitive functioning across
advancing age.

56
Contrary to predictions, individuals endorsing higher levels of openness did not
have an advantage in terms of rate of decline compared to individuals lower on openness.
For the most part, there was no relationship between openness and change over time.
Moreover, for women, higher openness was actually predictive of a faster rate of decline
over time on the block design cognitive task. The lack of support for the hypothesized
protective effect of openness on cognitive decline may also be due to the statistical
difficulty in having only one measurement point for openness and the subsequent loss of
predictive power over time. As can be seen in Table 7, the strength of the correlations
between openness and cognitive tasks declined over time; however, it did remain
significant.
The other personality trait predicted to have a protective effect on cognitive
decline was optimism. It was hypothesized that individuals endorsing higher levels of
optimism would both have an advantage on cognitive functioning and be protected
against faster rates of cognitive decline. Based on the stress-reduction hypothesis, it was
predicted that optimism would be associated with lower-stress, which in turn, would
protect against stress-induced declines associated with cognitive health and aging
(Fratiglioni et al., 2004; Spalosky, 1996; 2000). However, results indicated that neither
males nor females endorsing higher levels of optimism had better cognitive performance.
In terms of trajectories, only two models were significant and these varied by sex and by
cognitive task. For males, while higher optimism was associated with a poorer mean
performance on Information, optimism was protective over time, with slower rates of
decline in performance. For females, higher optimism was associated with a faster rate of

57
decline on the Thurstone’s Picture Memory task. These results may indicate that
optimism is simply not a strong predictor of cognitive functioning. Alternatively, it is
possible that from a cultural standpoint, optimism is perceived differently in Sweden. For
example, higher optimism may not be perceived as a positive coping resource or even a
socially encouraged trait. Such a cultural difference would explain the absence of
consistent results in the present study.
It was hypothesized that conscientiousness would be associated with higher
cognitive functioning due to the trait components of industriousness and need for
achievement. Previous research had suggested that conscientiousness was related to
educational attainment (Digman, 1972; Digman, 1989; Shiner et al., 2003). However, in
the present study, conscientiousness was not found to be positively correlated with
education, nor was it significantly positively correlated with any of the cognitive tasks
across any measurement occasions for females or males. Instead, males who endorsed
higher levels of conscientiousness were found to perform more poorly on the Block
Design and Information tasks. No relationship to longitudinal trajectories was predicted
but two isolated results emerged. Despite conscientiousness predicting poorer average
performance on the information task, for males, those who endorsed higher levels of
conscientiousness had a slower rate of decline. However, females who endorsed higher
rates of conscientiousness had a faster rate of decline on the Symbol Digit task.
These results are in line with some previous findings indicating a negative
relationship between conscientiousness and measures of cognitive functioning (Moutafi
et al., 2004; Moutafi et al., 2005). It may also be the case that conscientiousness, due to

58
an attentional component, may negatively affect cognitive performance by actually
slowing performance on speeded or timed tasks. This would be most noticeable tasks
such as Block Design and Symbol Digit, where more points are awarded for faster times.
Indeed, results contrary to hypothesis were observed on both of these tests. Such findings
suggest that conscientiousness cannot be ruled out as a protective factor in cognitive
aging as it may be confounded by processing speed which has been shown to decrease
with age (Finkel, Reynolds, McArdle, Pedersen, 2005; Lindenberger, 2001).
Agreeableness was not expected to result in an advantage on cognitive
performance or on longitudinal trajectories. As predicted, for females, higher
agreeableness was not associated with an advantage on cognitive performance or decline
compared to lower agreeableness. For males higher agreeableness was associated with a
poorer performance on the Information task, and males who were more agreeable had
faster rates of decline on the Symbol Digit task. These findings lend some support to
research by Baker and Bischel (2006) wherein cognitively superior older adults endorsed
significantly lower levels of agreeableness. Similarly, Schaie et al., (2004) found that
group dependency, or the tendency to be a follower and adhere to the group, was also
predictive of poorer cognitive performance. In relation to mechanisms of successful
cognitive aging, agreeableness might reflect a more passive approach to life. This
personality style may lead to fewer exposures to cognitively enriching experiences and
reflect weaker cognitive resources (Churchill et al., 2002). While the results of the
present study larger do not find a clear protective effect for lower agreeableness, there is

59
some suggestion that Swedish males who are less agreeable may be at an advantage for a
stronger base of learned knowledge.
Finally, it was hypothesized that for fluid abilities, personality would have a
greater impact on the trajectory of performance over time than on the average
performance level, while for crystallized abilities personality would have a greater impact
on the level of performance than on the trajectory over time. Overall, the results did not
support these predictions. For males, personality influenced performance on the
Information task, such that males who endorsed higher openness performed significantly
better whereas males endorsing higher optimism, conscientiousness, or agreeableness
performed more poorly. In terms of trajectories, for males, higher optimism and
conscientiousness were associated with a slower rate of decline on the Information task.
No consistent associations between personality and performance level or trajectories were
found for females.
In terms of fluid abilities, results were inconsistent. No effects of personality on
trajectories over time were found for Digit Span. Only openness (for both males and
females) was associated with a better average performance. No notable patterns for
performance or trajectories over time were revealed for Block Design, Symbol Digit, or
Thurstone’s Picture Memory.
In summary, the most notable and consistent finding for this study was the
relationship between openness to experience and cognitive performance. Even after
controlling for the effects of education, higher levels of openness provided a distinct and
significant advantage across all cognitive tasks for both men and women, and while rates

60
of decline were not found to differ between levels of openness, the superior performance
was maintained across advancing age. Previous research has suggested that individuals
who participate in more social and cognitive stimulating activities may be protected
against cognitive impairment (Wang et al., 2006) cognitive decline (Barnes et al., 2004;
Hultsch, Hertzog, Small, & Dixon, 1999; Newson & Kemps, 2005; Wilson et al., 2003)
and dementia (Wang et al., 2002; Wilson et al, 2002). While it is also possible that
openness to experience may only be a reflection of intellectual ability, it seems likely,
based on the components of openness, that individuals who endorse more openness may
be more actively and cognitively engaged with life. However, it is yet unknown how
positive personality traits are related to the active engagement hypothesis, and what, if
any, relationship they have in combination with successful cognitive aging.
Limitations
There were several limitations to this study. In general, effect sizes were very
small across all models of personality and cognition. For example, education accounted
for a much larger proportion of variance in cognitive performance than did personality.
Large sample sizes can sometimes over-power analyses, resulting in significant findings
of less clinical significance.
Beyond the previous interpretation of the relationship between openness and
cognitive performance, there could be other explanations as well. The trait of openness,
has also been termed “need for intellect”, “intelligence”, and “culture” by researchers
because of the curiosity component and high correlation with cognitive functioning. The
present study also found a strong positive correlation between openness and education for

61
both males and females. However, Swedish individuals included in this study often only
had access to the required elementary education (approximately 6 years). So while this
study controlled for education, education in this sample may not be the best proxy for
intellectual ability. Specifically, if this was the case, controlling for education may not
control for the effects of cognitive ability and this might explain the strong association
between higher openness and better cognitive performance.
Another limitation was that this study only considered personality from one
measurement occasion. In terms of a longitudinal study, this may have introduced
additional variation, because for some personality-trait combinations, there existed a
somewhat stronger correlation between an individual’s first personality measurement and
earlier cognitive measurements (IPT1-3) than the correlation between personality and
cognitive measurements taken at IPT5 and IPT6. This issue may have weakened the
results for performance level but would have had an even greater impact on the
trajectories over time. One way to address this limitation would be to evaluate dual
models of longitudinal change simultaneously for both personality traits and cognitive
performance. These dual models have been termed bivariate dynamic latent structural
equation models. Through these models, hypotheses and comparisons can be made about
parallel growth and proportional growth (McArdle et al., 2004). Similarly, since
personality was only measured once, the stability of personality was assumed and the
existence of intra-individual variation in personality over advancing age cannot be ruled
out.

62
Another concern in longitudinal studies is dropout. It is possible that individuals
who dropped out of the study, regardless of reason, may have had personality traits that
could have affected the results. For example, Reynolds and Pedersen (1997) examined
individuals in the SATSA data and found that individuals who had lower extraversion
scores and higher neuroticism scores were more likely to drop out of the study over time.
A final limitation is that the population of Sweden during the adult years of this
sample was quite demographically homogenous. Thus, the ability to generalizing these
findings to other populations may be limited.
Conclusion
The purpose of this study was to examine whether the personality traits of
openness to experience, optimism, conscientiousness, and agreeableness influenced
cognitive functioning at baseline and contributed to differences in trajectories of
cognitive functioning over time. As predicted, openness was the most consistent indicator
of cognitive performance. Both males and females endorsing higher levels of openness
performed significantly better across all five cognitive tasks and this advantage remained
stable over time. Differences in level of openness were not, however, associated with
rates of cognitive performance across advancing age. Optimism, conscientiousness, and
agreeableness were not found to affect cognitive functioning in any consistent pattern.
Findings were sometimes contrary to hypothesis, and results varied non-systematically
both by sex and by combination of personality trait and cognitive test.

63
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75
Appendix A

Personality Measures

Agreeableness Scale: This scale is computed by summing the items. Reverse scored items are
starred.

1. I often get into conflicts with my family or my colleagues. *
2. I like to put myself out to help others.
3. It doesn’t bother me to punish children or pets. *
4. Many people think that I am egotistical and self-centered. *
5. I would rather comply than to object.
6. I would rather co-operate than compete.
7. I don’t get upset when I think of the starving masses *
8. I have learned that one has to be prepared to defend one’s interests. *
9. I try to be polite to everybody.
10. I am often cynical and skeptical of other people’s intentions. *

Conscientiousness Scale: This scale is computed by summing the items. Reverse scored items are
starred.

1. I work hard to achieve my goals.
2. I like to keep everything in its place so that I know where things are.
3. I work hard towards achieving the goals I've set up for myself.
4. I am quite good at pacing my work in order to get things done on time.
5. I always pay all my debts in full when they are due.
6. I strive to achieve as much as possible.
7. I'm not particularly systematic. *
8. I like to keep everything clean and tidy.
9. I seem to be badly organized. *
10. I have difficulty in getting started on things. *

Openness to Experience Scale: This scale is computed by summing the items.

1. I like to solve problems or riddles.
2. I find it easy to empathize with others.
3. I have great intellectual curiosity.
4. I find it interesting to take up new hobbies.
5. I like to ponder on theories and/or philosophical ideas.
6. I often try out new and foreign foods.

Optimism Scale: This scale is computed by summing the items.

1. In hard times I usually hope for the best.
2. I always see the bright side of things.
3. I look optimistically to my future.
4. I believe in the saying "There is nothing bad that doesn't have something good about it".

76
Appendix B

Covariate Measures

Activities of Daily Living Scale (ADL)

1. Can use phone
2. Can go out of walking distance
3. Can shop for groceries/clothes
4. Can prepare meals
5. Can do own housework
6. Can take own medicine
7. Can handle own money
8. Can eat
9. Can dress and undress self
10. Can take care of appearance
11. Can walk
12. Can get in and out of bed
13. Can take a bath or shower
14. Can get to the bathroom on time

Cardiovascular Disorder Scale (CVD)

1. Have had angina pectoris
2. Have had heart infarct
3. Have had claudicatio
4. Have had high blood pressure
5. Have had heart insufficiency
6. Have had heart attack
7. Have had phlebitis
8. Have had circulation problems in limbs
9. Have had thrombosis
10. Have had a stroke
11. Have had tachycardia
12. Have had heart operation
13. Have had heart valve problem

Abstract (if available)

Abstract The purpose of this study was to examine whether personality traits affect cognitive functioning and rate of cognitive decline in older adults. Participants were 857 individuals from the Swedish Twin/ Adoption Study of Aging (SATSA). Data included four personality measures and longitudinal cognitive measurements. It was hypothesized that individuals who endorsed higher levels of conscientiousness, openness, and optimism would have higher cognitive test scores and lesser rates of cognitive decline, whereas agreeableness would not protect against cognitive decline. Latent growth curve models were fit to assess level of cognitive performance (intercept) and trajectories of cognitive performance over advancing age (slope). As predicted, higher levels of openness to experience were associated with a significantly higher performance across all cognitive tests for both males and females even after controlling for education. Agreeableness, as expected, but also conscientiousness and optimism, did not confer any consistent advantage on either cognitive performance or cognitive decline.

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Asset Metadata

Creator Schoenhofen, Emily Anne (author)

Core Title Personality and cognitive aging: are positive traits protective?

School College of Letters, Arts and Sciences

Degree Master of Arts

Degree Program Psychology

Publication Date 08/07/2007

Defense Date 04/25/2007

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag aging,cognitive decline,OAI-PMH Harvest,older adults,Personality

Language English

Advisor Gatz, Margaret (committee chair), Meyerowitz, Beth (committee member), Pedersen, Nancy L. (committee member)

Creator Email schoenho@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m765

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Rights Schoenhofen, Emily Anne

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