Age differences in the heritability of mean and intraindividual variation of psychological distress.

<p><b>BACKGROUND: </b>An important question in the study of intraindividual variability is whether the same explanatory mechanisms govern between person variation and within person variation.</p><p><b>OBJECTIVE: </b>This paper investigates genetic and environmental influences on affect across varying time frames and genetic and environmental influences on within person variation in affect.</p><p><b>METHODS: </b>Twin participants aged 25-74 years provided information on their affective experiences over monthly, weekly, and daily recall periods. Questionnaires and daily telephone interviews were used to assess frequency of negative emotions.</p><p><b>RESULTS: </b>Monthly, weekly, and daily reports of negative affect all showed modest genetic influence. Monthly and daily measures also demonstrated modest shared environmental influence. Sibling resemblance in within-person variation in affect was accounted for entirely by shared environment. Tests for age differences in magnitude of genetic and environmental effects revealed that genetic influences on monthly reports of affect were greater among older adults, but genetic influences on daily affective experiences were lower among older adults.</p><p><b>CONCLUSIONS: </b>Lowered heritability in daily affect among older adults contradicts standard behavior genetic expectations, and is consistent with the proposition that older adults gain skills in emotion regulation.</p>