The Mini-IPIP, a 20-item short form of the 50-item International Personality Item Pool-Five-Factor Model measure (Goldberg, 1999), was developed and validated across five studies. The Mini-IPIP scales, with four items per Big Five trait, had consistent and acceptable internal consistencies across five studies (= at or well above .60), similar coverage of facets as other broad Big Five measures (Study 2), and test-retest correlations that were quite similar to the parent measure across intervals of a few weeks (Study 4) and several months (Study 5). Moreover, the Mini-IPIP scales showed a comparable pattern of convergent, discriminant, and criterion-related validity (Studies 2-5) with other Big Five measures. Collectively, these results indicate that the Mini-IPIP is a psychometrically acceptable and practically useful short measure of the Big Five factors of personality.

Intraindividual personality variability is a construct that reflects the extent to which a person's self-reported personality changes over time or across social roles. Past studies have linked variability with important outcomes such as adjustment and well-being. However, existing variability measures conflate mean-level variance with true change over time, and thus these past findings are questionable. Three studies were conducted to examine the psychometric properties of existing variability indexes and to develop a new index that does not suffer from the problem of conflated variance. This new index is reliable and valid and can predict actual changes in self-reports over time. However, once mean-level variance is removed, intraindividual variability is no longer related to well-being.

Two large-scale, nationally representative panel studies (the German Socio Economic Panel Study and the British Household Panel Study) were used to assess changes in life satisfaction over the lifespan. The cross-sectional and longitudinal features of these studies were used to isolate age-related changes from confounding factors including instrumentation effects and cohort effects. Although estimated satisfaction trajectories varied somewhat across studies, two consistent findings emerged. First, both studies show that life satisfaction does not decline over much of adulthood. Second, there is a steep decline in life satisfaction among those older than 70. The British data also showed a relatively large increase in satisfaction from the 40s to the early 70s. Thus, age differences in well-being can be quite large and deserve increased empirical and theoretical attention.

Six mood induction studies and a meta-analysis were conducted to test 2 models of the extraversion-pleasant affect relation. The affect-level model suggests that extraverts should be happier than introverts in both neutral and positive mood conditions. The reactivity model posits that extraverts react particularly strongly to pleasant stimuli and that they should be happier than introverts only in positive conditions. In all studies, extraverts failed to exhibit greater emotional reactivity when pleasantness items were analyzed. When activated positive affect items were analyzed, results were mixed. The meta-analysis confirmed that there is only a slight reactivity effect overall, and this effect emerges only in activated positive affect items. Furthermore, the meta-analysis showed that the correlation in neutral conditions is strong enough to support the affect-level model.

Although personality psychologists often focus on between-person differences, understanding intraindividual variability is also a critical focus of the subdiscipline. Despite the fact that non-self-report techniques exist for assessing variability, questionnaire-based measures are still the norm. In two studies (N = 149 and N = 202) we examine the possibility that intraindividual variability measures derived from repeated self-report assessments are affected by certain response styles. These studies, which use a variety of techniques for assessing within-person variability, show that standard measures are moderately to strongly correlated with theoretically unrelated variability measures, including those based on ratings of satisfaction with neutral objects or the personality of cartoon characters. These results raise questions about the validity and utility of widely used measures for assessing intraindividual variability.