Evidence for an independent syndrome of hyperactivity.

It has recently been suggested that hyperactivity and an aggressive conduct disorder cannot exist independently in children. The results of a factor analysis of the Conners Teacher Rating Scales of over 9000 children provided preliminary evidence to the contrary; a hyperactivity factor emerged as explaining the greatest proportion of the variance. Because of the large size of our data-set, it was deemed necessary to investigate the heuristic value of this finding. Using norms calculated on composite factor scores, a contingency analysis was performed to determine the proportions of children who were above a two-standard deviation criterion of deviance on all factors and combinations of factors. The use of different degrees of statistical control produced prevalence estimates comparable to those reported in the literature. These findings raise the possibility that studies reporting different prevalences of hyperactivity may, in fact, be exercising different degrees of conservatism in classification. Also, when the extent of overlap along each of our factor dimensions was examined, a group of children who appeared to be hyperactive but not conduct-disordered emerged. These findings provide evidence for an independent syndrome of hyperactivity in a sample of Canadian children.