Birth-order and sex differences in the frequency of referral of children for psychological treatment: A partial replication and extension

Abstract

A previous study of two-child families by Lahey, Hammer, Crumrine, and Forehand (1980) found that firstborn children were more likely to be referred for psychological treatment than second-borns and that males were more likely to be referred than females. Furthermore, there was a significant interaction between these two variables. In the present study, a new sample of two-child families from the same clinic was studied, confirming the previous findings of significant birth-order and sex effects but not the interaction. Separate analyses indicated that both birth-order and sex effects were significant for children given “externalizing” diagnoses, but only the birth-order effect was significant for heterogeneous “internalizing” diagnoses. Similarly, an analysis of only children revealed a significant sex effect for externalizers but not internalizers. A combined sample of two-child families independent of diagnosis (N=425)suggests that there are reliable associations of birth order and sex, but not the interaction, with referral rates in two-child families. Referred children were significantly more likely to have a female sibling than would be expected by chance, regardless of birth order or sex, suggesting that these children may look more deviant by comparison to female, vs. male, siblings, thus increasing the likelihood of clinic referral. The potential utility of birth order and sex as “demographic marker variables” for etiological research is discussed.