Objective III. Do predictors differ between young and old age depression and quality of life?
STRENGTHS AND WEAKNESSES
Strengths of this study include the assessment of all five factors of personality and the demonstration of a personality-depression relationship after adjustment for socio-demographic and especially physical comorbidity characteristics. Indeed, univariate and multivariate models did not generate the same results with respect to personality dimensions. Further, its clinical relevance lies in the fact of not only considering psychiatric diagnosis of mood disorder to characterize depressive episode, but also to consider patients’
subjective experiences, as assessed by the level of their perceived quality of life. Most importantly, strengths include the consideration of two distinct age groups with matched clinical backgrounds for young and old participants with respect to their recurrent nature and length of episodes, the presence of past hospitalizations and family history, the community based outpatient treatment setting, as well as careful exclusion of other psychiatric disorders in all participants by trained clinicians using well-established investigator-based assessment procedures. The narrow focus on nonpsychotic major depression rather than the whole depression spectrum allowed for a more homogenously defined and clinically relevant outcome.
Several limitations should, however, be taken into account. Even though the planned sample size was achieved, the sample size remained too limited to perform overall statistical analyses that would have included all study variables into one model. Plus, the reduced number of old age patients did not allow for performing separate comparisons of late- and early-onset nature of depression. Indeed, several authors revealed differences with regard to their interplay with personality (Boyd et al., 2000; Brodaty et al., 2001). As mentioned,
early-onset depression has been more frequently associated with personality characteristics, while onset depression was related to vascular burden. Running all analyses without the late-onset patients would have reduced the small sample size even more. A better option would have been to retain age of onset (< 60 years) as an additional inclusion criterion, even though this would have lengthened the recruitment process. Plus, several additional independent variables, such as genetic substrates of personality traits (DNA methylations and epigenetic expression of the 5-HTTLPR gene), coping strategies, or leisure activities, known to play a predominant role in old age depression outcome studies, have not been included in the present study (Jones et al., 2003; Waddell & Jacobs-Lawson, 2010; Weber et al., 2011). Further, exposure to life stress was elicited retrospectively and after disease onset, thus a reporting bias cannot be excluded. Also, the cross-sectional design did not allow for completely solving the state-trait debate on Neuroticism. Future longitudinal studies in larger samples of older depressed patients addressing these limitations are clearly needed to explore the validity of the present observations. While depressive illness was observer-rated and personality self-rated to avoid that common method variance inflates their association, quality of life was self-rated. However, previous studies in younger samples considered the threat of common method bias to be minimal (Schimmack et al., 2004; Watson et al., 2000). These authors found a high positive correlation between self and informant reports of life satisfaction and revealed that personality variables accounted for 60% of the shared variance between the two measures. The main limitation concerns the age distribution. Rather than remain faithful to the initial research plan of four distinct groups, it would have been best to redesign the study to include only two groups of depressed patients and never-depressed controls without controlling for age criteria and to assess age as a continuous variable.
CONCLUSIONS
Results of the present study showed that personality factors and depression are related, independently of patients’ age. Differences in this relationship were mainly due to the intensity of depressive symptoms rather than the patients’ life period. Evidence suggested that major depression is a multifactorial disorder, influenced by a series of both risk and protective factors. Higher depressive symptoms were related to high physical burden, negative subjective impact of stressful life events and only to one personality factor, namely high Neuroticism, at least during acute depressive episodes. In contrast, when opposing old to young age depression, it was the combination of increased physical illness and low depressive symptoms that best differentiated depression in old age from young age. The impact of Neuroticism and stressful life events was tempered in later life.
Results further confirmed a strong relationship between depressive symptoms and subjective quality of life. While the integration of the five personality dimensions added no significant information for depression prediction, their inclusion revealed to be a promising approach when addressing the question of the influence of the depressive episode on patients’ quality of life. In addition to high Neuroticism, which lowered quality of life, Openness to experience and Conscientiousness showed a significant protective influence, and Neuroticism and Conscientiousness additionally interacted with depression to enhance patients’ quality of life. Further, quality of life predictors differed according to participants’
age. In younger adults, well-being was exclusively influenced by the intensity of depressive symptoms. In contrast, in older adults well-being was additionally decreased by higher suicide risk, higher physical illness and protected by personality factors. Openness and Agreeableness showed a direct influence on quality of life, while Openness and Conscientiousness acted indirectly by interacting with depression. Personality dimensions revealed to be promising predictors when addressing patients’ subjective perception of well-being in relation to late life depression. Indeed, personality traits have been shown to influence the frequency of service utilizations in old age primary care (Chipperfield &
Greenslade, 1999).
In extension to existing evidence, results from the present study allowed for reproducing the association between Neuroticism and depression in a case-control comparison including age-matched never-depressed controls rather than the limited comparison with published instrument norms. Indeed, norms of the French NEO PI-R are based on a selective reference sample of 801 adults with a mean age of 31.69 (11.29) years and include only 9%
of adults aged 65+ (Rolland, 1998). The inclusion of two distinct age groups showed the relative importance of stressful life events and physical comorbidity according to patients’ life periods. Besides, data revealed that stressful life events do not play a significant role in themselves, but rather their subjectively perceived emotional impact. Interestingly, besides gender, characteristics such as education, marital status, social support, or loss of autonomy are of little importance in influencing both depression and quality of life, independently of individual’s age, when physical health status and personality are simultaneously considered.
Regarding future research directions, analyses on all 30 NEO PI-R facets were not possible in the present study given the limited sample size. However exploratory analyses revealed promising results. Indeed, specific personality facets were stronger predictors of symptom severity than their higher-order factors, such as the presented Depression facet (N3) and Self-Consciousness (N4) of Neuroticism, but also the Positive Emotion facet (E6) of
Extraversion, the Openness to action (O4) facet of Openness, the Trust facet (A1) of Agreeableness and the Competence facet (C1) of Conscientiousness (data not reported).
Previous studies in younger samples have also revealed that the Depression facet and the Positive emotion were stronger predictors of life satisfaction than their corresponding factors (Schimmack et al., 2004).
General prevention and treatment of depression interventions are costly and lack a person-centred focus, whereas selective interventions are true preventive measures that are cost effective and can be tailored to an individual patient. However, implementation of such selective strategies requires knowledge of risk factors and causal processes that lead from the individual vulnerability to the disorder. As Klein et al. (2011) stated, the majority of risk factors are immutable (e.g. physical illness) or predict depression in the short term (e.g.
stressful life events), while personality is malleable by psychotherapeutic interventions and may forecast recurrence of depression in advance, which makes it possible to identify individuals at risk, and to establish adapted treatment plans.
Thus, studies on the relationship between depression, well-being and personality may gain from enlarging their focus on integrative approaches, including physical comorbidities and psychological vulnerability factors, such as the Five-Factor Theory of personality. The richness of building multivariate explanatory models when studying the determinants of depressive episodes and associated well-being was confirmed. Integrative frameworks including not merely traditional socio-demographic and psychosocial predictors, but also intrapersonal features, and even more the combination of several factors, are a complex but promising approach. For mental health clinicians, these predictors are of crucial importance because of the main focus on psychotherapeutic processes. Indeed, the few existing studies showed quite clearly that personality traits can be changed as a result of therapeutic interventions (Bagby et al., 1995; De Fruyt et al., 2006; Trull et al., 1995). Indeed, as Roberts et al. (2008) pointed out, compared to the one standard deviation of magnitude of personality trait change that occurs across the life course, changes obtained after 6 months of psychotherapy might be of quite dramatic magnitude, and reach an equal of 20 years of natural progression in personality development.
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