title: Birth order has no effect on intelligence: a reply and extension of previous findings.
abstract: We address points raised by Zajonc and Sulloway, who reject findings showing that birth order has no effect on intelligence. Many objections to findings of null birth-order results seem to stem from a misunderstanding of the difference between study designs where birth order is confounded with true causal influences on intelligence across families and designs that control for some of these influences. We discuss some of the consequences of not appreciating the nature of this difference. When between-family confounds are controlled using appropriate study designs and techniques such as multilevel modeling, birth order is shown not to influence intelligence. We conclude with an empirical investigation of the replicability and generalizability of this approach.
authors.affiliation: The Ohio State University, USA. wichman.3@osu.edu
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; D005191:Family Characteristics; D006801:Humans; D007360:Intelligence; D008962:Models, Theoretical; D014481:United States