Birth Order Studies: Some Sources of Bias

Abstract

“… they both felt, after the conclusion of their work, very doubtful as to the possibility of definitely proving the existence of a real differential incidence of any character in order of birth. The whole question seemed so open to fallacious possibility in different directions.”[Report of comment by G. Udney Yule in the discussion following his joint paper with M. Greenwood at the Royal Statistical Society in 1914.]Recently there has been an upsurge of interest in the association between behaviour, both normal and abnormal, and birth order. For instance, Barry (1967) has pointed out that in certain societies excessive parental demands are made on the first-born child, and “excessive parental demands could lead to superior achievement in a robust individual or to psychiatric illness in a child who was especially vulnerable …”; thus putting into modern language an interesting genotype-environment interaction which was summed up in the ancient Chinese proverb “fire burns wood but tempers iron”.