Main effects or transactions in the neuropsychology of conduct disorder? Commentary on “The neuropsychology of conduct disorder”

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Abstract
In this commentary, we (a) discuss logical and empirical limits on the transactional model in accounting for the etiology of any developmental psychopathology, including conduct disorder (CD), and (b) review evidence bearing on whether or not frontal lobe lesions can directly produce CD behavior. Logically, transactions can both decrease and increase phenotypic variance; moreover, there is a mathematical limit (50%) to the amount of variance for which they can account. Empirically, documenting a transactional effect requires (a) that we have unconfounded measures of a child's biotype and social environment, (b) that the biotype and social environment are correlated, and (c) that we have a design (such as an adoption design) that is capable of separating the contribution of this correlation to outcome variance from the main effects of either biotype or social environment considered separately. Given these limits, we should also look for main effects in the etiology of CD. We argue that early damage or dysfunction in the frontal lobes may be one such plausible main effect on CD.