the ODD never CD and ODD→CD pathways. Second, the CAPA uses a three-month reporting period. As a result, annual assessments may miss some periods of disorder and therefore underestimate prevalence in the population. This may be particularly relevant for CD as DSM-IV requires symptoms to be present at any point in a 12 month timeframe, so long as one is present within the previous 6 months. In addition, year-on-year fluctuations (whereby cases fall just above and just below diagnostic thresholds) have been reported even in clinical samples (Burke, in press). Each of these factors could have contributed to an underestimation of rates of disorder. To the extent that cases of ODD were missed we may have overestimated the proportion of cases in the CD only pathway. To the extent that cases of CD were missed, we may have overestimated proportions in the ODD only group. In practice, however, we know of no evidence to suggest that the CAPA substantially underestimates either ODD or CD diagnoses. Comparative studies show no systematic difference between prevalence estimates derived from the CAPA and from other diagnostic approaches (Maughan et al., 2004). It is possible that measurement artifacts may have led to some underestimation of
