The independence of hyperactivity from conduct disorder: methodological considerations.

It has been claimed that the childhood behavioural factors "hyperactivity" and "conduct disorder" are highly correlated. The fact that hyperactive symptoms load heavily on the conduct disorder factor has also been used to support the notion that hyperactivity is not an independent behavioural dimension. The present study employs a large sample of combined clinic and normal children to demonstrate that both of these observations are artifacts of methodological technique. When factor score coefficients are used to interpret factors, the hyperactive symptoms do not load on the conduct disorder factor. If factor scores are defined by the use of unit weights, as in previous studies, then the intercorrelation between the hyperactive and conduct disorder factors is high. The use of factor score coefficients to define factors, on the other hand, produces uncorrelated factors. The results support the idea that hyperactivity and conduct disorder are independent behavioural dimensions.