A comparison of twins and singletons with child psychiatric disorders: an Item Sheet study.

An important assumption underlying the twin method of comparing MZ and DZ twins is that results from twin samples can be generalized to the larger singleton population. This study uses Item Sheet data on child psychiatric patients to compare twins and singletons on demographic, diagnostic and symptomatic variables. Although little difference was found between the two groups, conduct disorders were significantly over-represented in the twin population. The significance of this finding is discussed. This study lends overall support for the use of the twin method in child psychiatric samples.