Obtained objectively assessed measures of activity, fidgeting, vigilance, selective attention, and aggression for a sample of 87 twin pairs in late childhood (mean age 7.6 yrs). Data included videotaped observations in standardized situations, objective test scores, and mechanical measures. Test–retest reliability was obtained for all measures. Contrary to results of questionnaire studies, there was little evidence for genetic influence on reliable and objective behavioral assessments. Also in disagreement with questionnaire studies, between-family environmental sources of variance were far more important than within-family factors.
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Plomin et al. (1980) studied this question.
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