obtained by more anonymous means of as sessment.35 Furthermore, several prior studies support the validity of self-report assessment of CD.36-38 Fourth, CD symptoms were reported retrospectively. We can not, therefore, rule out a substantial effect of memory bias. It is, however, difficult to construct a plausible scenario in which monozygotic twins are more highly correlated than dizygotic twins in their biases for recall of some items (those loading on the 2 genetic factors) while equally correlated in their biased recall for other sets of items (those loading onto the common environmental factor). Furthermore, Nock et al recently reviewed the literature on retrospective reports of CD symptoms and concluded that, despite evidence for underreporting of less deviant behaviors, “…adults recall childhood experiences with sufficient accuracy to provide useful information in retrospective studies.”39(p708) Fifth, our modeling assumed that genetic and environmental factors acted additively on risk for CD symptoms and were uncorrelated. Finally, few subjects in our sample endorsed large numbers of CD criteria. Thus, most of the information used in our analyses comes from individuals with modest numbers of symptoms.
