Finally, the effect sizes were derived from published studies that assessed individuals from different cohorts that grew up in different periods. It may be the case that the genetic and environmental influences on personality not only depend on the chronological age of an individual, but also depend on the macro-environmental context that changes across cohorts or periods (e.g., Heath et al., 1985). Identifying these types of temporal trends would be highly novel research for personality psychology. In the context of the current study, we assume that age differences across longitudinal studies converge to provide a reasonable viewpoint of the larger lifespan trend (Bell, 1953). The alternative to this limiting assumption is to track a single cohort through the lifespan to examine the differential stability of personality, but no such sample is available.
