Birth Order Has No Effect on Intelligence: A Reply and Extension of Previous Findings

¹ The Ohio State University
² University of Oklahoma
³ University of North Carolina–Chapel Hill

^* To whom correspondence should be addressed. E-mail: wichman.3{at}osu.edu.

	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.

First published on July 26, 2007, doi:10.1177/0146167207303028

Personality and Social Psychology Bulletin 2007;33:1195.

A more recent version of this article appeared on September 1, 2007


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