behaviours. This work suggests that our thoughts and feelings about performing a
particular health behaviour (e.g. exercising) are a primary determinant of whether we
perform that behaviour. That is, we tend to engage in behaviours that we have positive
thoughts and feelings about (see Chapter 7). Consequently, conscientiousness may
influence the amount of exercise we do by shaping our thoughts and feelings about
exercising (i.e. thoughts and feelings mediate the impact of conscientiousness on
exercise). Such mediation effects have been demonstrated by Siegler et al. (1995), who
found that the effect of conscientiousness on mammography attendance was mediated
by knowledge of breast cancer and the perceived costs of seeking mammography.
Similarly, the impact of conscientiousness on the self-care activities of patients with
type 1 diabetes has been found to be mediated by treatment beliefs (e.g. Christensen,
Moran and Wiebe, 1999). However, other research has found both mediated and direct
effects for conscientiousness when predicting health behaviour (Conner and Abraham,
2001; O’Connor et al., 2009; Vollrath, Knoch and Cassano, 1999).
In addition to mediation effects, conscientiousness might also operate as a moderator
changing the relationship between health beliefs and health behaviour patterns. A few
studies have examined the moderating role of conscientiousness. For example, in a
retrospective study, Schwartz M.D. et al. (1999) found that conscientiousness moder -
ated the relationship between breast cancer-related distress and mammography uptake
such that, among those with high levels of distress, those with high conscientiousness
scores were more likely to have attended mammography screening than those with
low conscientiousness scores. Conscientiousness scores had no effect on attendance
among those with low levels of distress. Hampson et al. (2000) reported a similar
significant interaction between conscientiousness and perceived risk in relation to
changes in indoor smoking behaviour in response to the threat from radon gas, with
greater response to risk among the more conscientious. In relation to exercise, Rhodes
PERSONALITY AND HEALTH 131TABLE 6.1Relationship between conscientiousness and various health behaviours based
on a meta-analysis of available studies
Behaviour Effect size Total sample size
Physical activity .05 24,259
Excessive alcohol use –.25 32,137
Drug use –.28 36,573
Unhealthy eating –.13 6,356
Risky driving –.25 10,171
Risky sex –.13 12,410
Suicide –.12 6,087
Tobacco use –.14 46,725
Violence –.25 10,277
Note: Cohen (1992) suggests that r= 0.1 equates to a small effect size, 0.3 to a medium effect size and
0.5 to a large effect size; so these effect sizes for conscientiousness are mostly in the small to medium
range.
Source: From Bogg and Roberts (2004). Copyright © 2004 by the American Psychological Association.
Reprinted with permission.