Although these potential limitations may lead to an underestimate of the prevalence of TS and CT in the ALSPAC sample, our results are consistent with other prevalence estimates of TS and CT in the general population, and this study is one of few to report the overlapping rates of co-occurring TS/CT, OCD, and ADHD in a population-based sample. Furthermore, this is the first study to examine the rates of TS and CT in the ALSPAC cohort, in which detailed longitudinal data about child development are available for more than 7,000 children. Through our strict inclusion/exclusion criteria and heterogeneity analyses, we believe that we have identified optimal disease definitions that both meet DSM-IV criteria and maintain face validity. Therefore, these definitions should prove extremely useful for future studies of TS and CT in this cohort.
