ALSPAC children were evaluated for the presence of a tic disorder in nine mother-completed questionnaires from age 1.5 to 13 years (questionnaires are available at the ALSPAC Web site at http://www.bristol.ac.uk/alspac/sci-com/quests/). At yearly intervals from age 1.5 to 7.5 years and at age 10, mothers were asked a single screening question about the presence and frequency of “tics or twitches” in their child. Rates of positive response to this single tic question at each age are provided online (Table S1, available online). At age 13 years, a more detailed tic assessment was administered, including a section with five questions about specific motor and vocal tics: (C1: In the past year, has your child had any repeated movements of parts of the face and head (e.g., eye blinking, grimacing, sticking tongue out, licking lips, spitting)?; C2: Has your child had repeated movements of the neck, shoulder or trunk (e.g., twisting around, shoulder shrugging, bending over, nodding)?); C3: Has your child had repeated movements of arms, hands, legs, feet?; C4: Has your child had repeated noises and sounds (e.g., coughing, clearing throat,
