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A multilevel approach to the relationship between birth order and intelligence.

Wichman AL, Rodgers JL, MacCallum RC

Department of Psychology, The Ohio State University, USA.

Many studies show relationships between birth order and intelligence but use cross-sectional designs or manifest other threats to internal validity. Multilevel analyses with a control variable show that when these threats are removed, two major results emerge: (a) birth order has no significant influence on children's intelligence and (b) earlier reported birth order effects on intelligence are attributable to factors that vary between, not within, families. Analyses on 7- to 8 - and 13- to 14-year-old children from the National Longitudinal Survey of Youth support these conclusions. When hierarchical data structures, age variance of children, and within-family versus between-family variance sources are taken into account, previous research is seen in a new light.

Published 30 November 2005 in Pers Soc Psychol Bull, 32(1): 117-27.
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