Do non-shared environmental influences persist over time? An examination of days and minutes.

Non-shared environmental influences show only minimal stability over time prior to adulthood. The long assessment lags (typically 3-5 years) that characterize most longitudinal twin studies, however, make it difficult to interpret these results. To more rigorously evaluate non-shared environmental stability prior to adulthood, we fitted biometric correlated factors models to (1) seven consecutive days of self-reported negative and positive affect in 239 twin pairs aged 16-25 years and (2) seven consecutive minutes of observer rated warmth and control in 687 twin pairs aged 6-10 years. We then empirically examined patterns of etiologic stability over time using a mixed effects analog to the one-way ANOVA. Genetic and shared environmental correlations were found to be highly stable over both days and minutes. By contrast, non-shared environmental correlations decreased monotonically with increasing lag length, and moreover, were small-to moderate in magnitude when examining intervals longer than a few minutes. Such findings imply that the non-shared environment may be comprised primarily of transient and idiosyncratic effects prior to adulthood.