The study findings add to the limited research regarding personality and self-rated mental and physical health in people with chronic illnesses. They also provide new information on the potential moderating role of personality on the effects of chronic illness self-management interventions.
Regarding the baseline relationships, as hypothesized, trial participants with the distressed personality profile (Chapman et al., 2007b
) – higher neuroticism and lower agreeableness, conscientiousness, and extraversion – had lower baseline self-rated mental health, as measured by the MCS-36, than those with the opposite standing on these factors. Also as predicted, the strongest of these associations was for neuroticism.
These findings are generally consistent with those of the only prior study to examine this issue, which involved Dutch out-patients with mood and anxiety disorders. That study found a comparably strong association between neuroticism and MCS-36 scores, with weaker associations between extraversion and openness and MCS-36 scores and agreeableness and PCS-36 scores (van Straten et al., 2007
). Prior research has linked higher levels of neuroticism to psychological distress and mood and anxiety disorders (Jylha & Isometsa, 2006
; Kendler, Gatz, Gardner, & Pedersen, 2006
). Individuals high in neuroticism tend to be more aware of and/or more likely to raise concerns about their health than others (Kressin, Spiro, & Skinner, 2000
). The findings of the current and prior study suggest this tendency towards increased perception and/or reporting of health concerns may be greater in relation to psychological than to physical concerns.
Considerable differences in study samples and methodology probably contributed to the differences in findings related to effects of personality factors other than neuroticism on mental and physical health status in the prior and current study. In particular, the lack of association between baseline personality and physical health status in our study could reflect the mitigating influences of our study chronic illnesses, which were less prevalent in the Dutch study sample. Duration of diagnosis might also have played a role: most of our participants had been living with their chronic conditions for some time, and the influence of personality on self-rated health may vary at different points in the chronic illness trajectory.
Regarding effects of the intervention, there was a short-term main effect of in-home (but not telephone) HIOH on self-rated mental health: 4 and 6 week MCS-36 scores were significantly better in the home intervention group as compared with others, an effect that attenuated by 6 months follow-up. HIOH had no significant effects on self-rated physical health at any follow-up point. While the reasons for this finding are not fully clear, it may in part reflect sample homogeneity or temporal issues, as the role of personality might vary at different points in the chronic illness trajectory. It may also be that the small to moderate effect of the intervention on illness management self-efficacy (effect size 0.3) is not of sufficient magnitude to lead to significant changes in physical health and functioning. Finally, self-efficacy is conceptually more closely related to mental than physical health (Bandura, 1997
). The only prior 1-year RCT of a CDSMP variant also found only short-term effects on self-rated health (with respondents rating their health globally as excellent, very good, good, fair, or poor on a single question), with no effects at 1 year (Lorig et al., 2006
). Though comparisons between the studies are limited somewhat by their use of different self-rated health measures, it appears the CDSMP and its variants may result in small to moderate and relatively short-term effects on self-rated health, possibly limited to effects on mental health.
In partial support of hypotheses regarding moderating effects of personality, analyses revealed short-term benefits of the home intervention on MCS-36 scores were present only in those with low conscientiousness, an interaction that attenuated by 6 months. This finding echoes the results of the prior interim analysis from the RCT, which found beneficial effects of in-home HIOH on illness management self-efficacy were confined to patients lower in conscientiousness (Franks et al., 2009
). There are several possible explanations for these findings. First, low conscientiousness individuals tended to have lower illness management self-efficacy at baseline than did other participants in the RCT, regardless of study arm. Thus, they appeared to have the most room for improvement in self-efficacy, the putative mediator of illness self-management interventions such as HIOH, and when assigned to an intervention that aggressively targeted this deficit, both self-efficacy and self-rated mental health improved.
Additionally, dispositional tendencies that cluster under the conscientiousness category may affect the way participants perceive and respond to specific components, demands, and features of interventions like HIOH (Christensen, 2000
). For example, core dispositional elements of conscientiousness are self-control, organization, and goal-orientation. Low levels of these tendencies are likely to give rise to worse health behaviours within the disease self-management domain, including poor diet and exercise habits (Bogg & Roberts, 2004
; Goldberg & Strycker, 2002
; Roberts, Walton, & Bogg, 2005
). Several aspects of the HIOH intervention would appear particularly beneficial to individuals low in conscientiousness. For example, the concept of ‘action planning’, or setting and periodically re-evaluating and revising personal health goals, is emphasized throughout the intervention. This instructive scaffolding may have been particularly useful to less conscientious persons, who tend to be disorganized, have lower levels of self-control, and are less likely to set and follow through with goals. Gaining mastery of such habits may foster improved mental health. Such hypotheses remain speculative, since they were not tested in the current study. Future studies might examine whether the components of chronic illness self-management interventions interface with participant dispositional tendencies.
None of the other three factors that make up the distressed personality type – agreeableness, extraversion, and neuroticism – significantly moderated short-term intervention effects on MCS-36 scores, though indicates there were nonsignificant trends in this direction. The reasons why the study findings did not support hypothesized moderating effects of these three personality factors on self-rated mental health are not clear, though again the small to moderate effect of the intervention on self-efficacy may have played a role. The absence of personality moderation of intervention effects on self-rated physical health scores is perhaps not surprising, since the concept of self-efficacy is again more closely related to mental than physical health (Bandura, 1997
). Alternatively, this finding might primarily reflect the lack of HIOH intervention effects on physical health status in our sample in general.
Identification of patients more or less likely to benefit from chronic disease interventions can facilitate allocation of resources towards suitable candidates, improving the interventions' efficiency, or ratio of clinical benefit to delivery effort (Issel, 2004
). The utility of targeting medical interventions to those most likely to benefit is well-established, though it has thus far primarily been employed to guide prescription drug therapy. For example, a widely employed evidence-based algorithm to determine the need for and intensity of drug therapy for hyperlipidemia encourages careful consideration of each individual's overall risk for cardiovascular disease, rather than basing treatment solely on serum lipid values (National Cholesterol Education Program, 2001
). Our findings suggest this approach might also be useful in targeting illness self-management interventions to those most likely to benefit – in the case of HIOH, individuals low in conscientiousness. Brief (≤ 5 min to administer), valid, and reasonably reliable personality measures have been developed that could facilitate such targeting in clinical settings (Benet-Martinez, 1998
; Gustavsson, 2003
Future trials of chronic illness self-management interventions might block or stratify on participants' conscientiousness standing, and/or explore the utility of offering alternative versions of the interventions to those who the current results suggest are unlikely to respond favourably to the ‘standard’ programmes. The goal would be to begin to shift the emphasis from exclusively studying whether or not such interventions ‘work’ to determining in whom they are likely to be most effective.
This study had some limitations. It involved a sample of chronically ill out-patients who volunteered for a RCT, which may limit generalizability to other groups and settings. Mean MCS-36 and PCS-36 scores were somewhat lower than in the general population (Ware, Kosinski, et al., 1995
). Likewise, mean neuroticism scores were somewhat higher and mean scores for the other FFM factors somewhat lower than in the general population (Costa & McCrae, 1992
). Women were also slightly overrepresented compared with the general primary care population, in part due to the higher prevalence of depression (one of the six study diagnoses) in women relative to men (Kuehner, 2003
). Finally, several hypotheses were examined, raising the possibility of chance findings due to multiple hypothesis testing. However, the consistency of the current results with those in two prior relevant studies involving the distressed personality profile suggests it is unlikely our findings arose due to chance.
In conclusion, this study found significant relationships between several FFM personality factors and self-rated mental health, but no significant relationships between personality and self-rated physical health. Participants in a RCT of an illness self-management intervention with the distressed personality profile – higher neuroticism and lower agreeableness, conscientiousness, and extraversion – had worse baseline self-rated mental health than participants with opposite standing on these factors. Additionally, one of the FFM factors, conscientiousness, was found to moderate the short-term beneficial effects of the illness self-management intervention on self-rated mental health, with non-significant trends observed for the other three factors in the distressed profile. The differences observed in study findings for self-rated mental versus physical health emphasize the importance of employing measures that separately capture each facet when examining relationships among personality, intervention effects, and self-rated health. They also underscore the need for additional studies exploring such relationships, involving a wide array of study designs (e.g. observational vs. interventional), samples, and settings, to determine whether important contextual differences in associations may exist.