lower maternal age, and lower socio-economic status) are likely to predict nonparticipation in most epidemiologic studies. We may also have missed some subjects who had chronic tics that abated before age 13, the time point for which we have the most reliable tic-related data; however, because TS generally begins early in childhood and peaks in early adolescence, we believe that we have successfully captured most subjects.2 In addition, we deliberately chose rigorous disease definitions and sought to exclude subjects with likely non-tic movement disorders (e.g., stereotypies in autism or intellectual disability, repetitive arm/leg movements that could be better explained by tremor or motor restlessness) to minimize the potential impact of our necessary reliance on maternal questionnaires.
