title: A multilevel approach to the relationship between birth order and intelligence.
abstract: 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.
authors.affiliation: Department of Psychology, The Ohio State University, USA.
authors.forename: Aaron L
authors.initials: AL
authors.lastname: Wichman
authors.forename: Joseph Lee
authors.initials: JL
authors.lastname: Rodgers
authors.forename: Robert C
authors.initials: RC
authors.lastname: MacCallum
mesh_terms: D000293:Adolescent; D001722:Birth Order; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007360:Intelligence; D008297:Male; D008960:Models, Psychological