Diagnoses of TS and CT were defined by applying DSM-IV-TR criteria to the questionnaire responses based on three levels of stringency (Narrow, Intermediate, and Broad) (Table 1). Positive responses regarding the presence and frequency of specific motor and/or vocal tics in the Age 13 questionnaire were required for all definitions (Table 1). Positive responses at an additional time point between ages 1.5 and 10 years were required to meet DSM-IV-TR chronicity criteria of tic persistence for more than 1 year for the Narrow and Intermediate definitions. No chronicity criteria were required for the TS Broad definition. All assessments were performed before age 18 and thus met DSM-IV-TR age of onset criteria. Subjects who endorsed only repeated movements of the arms, hands, legs or feet (Question C3) or repeated words or phrases (Question C5) in the absence of a positive response to other tic questions (C1, C2, C4) were excluded from all case definitions to remove non-tic movements such as stereotypy or isolated echolalia. Response rates to each of the age 13 tic-related questions are provided online (Table S2, available online).
