Family Configuration and Mental Ability: Two Theories Contrasted with U. S. Data

Abstract

Recent articles have argued that family size and birth order have important cognitive influence, and may partially explain the different performances of social class and ethnic groups. Support for such claims has often depended on the analytic strategy, which has concentrated on the means of aggregated groups with large N’s. For the present analysis, data are reviewed from the massive U. S. National Longitudinal Study of Educational Effects. Results from aggregate analysis are quite similar to those reported by Zajonc and others. When individual variation is explored, however, the effects of family configuration become relatively trivial, and the confluence theory appears untenable. The apparent effects of family size, far from explaining population differences, seem themselves to be better explained as the result of group admixtures. And the small, residual birth-order effects therefore appear to result from other phenomena, still to be explained.