Figure 1 documents the flow of subjects through the study. Of 14,472 subjects with known birth outcomes, mothers of 7,152 subjects completed the age 13 questionnaire containing the detailed tic-related questions. Of these, 384 were excluded for ID, autism, IQ<80, or an SEN statement as described above, leaving 6,768 subjects for analysis (Figure 1). Point prevalence estimates of TS and CT at age 13 were calculated for the Narrow, Intermediate, and Broad definitions (Table 2). The prevalence rates for TS Narrow and TS Intermediate (0.3% and 0.7%, respectively), as well as CT Narrow and CT Intermediate (0.5% and 1.1%) were consistent with those reported in previous community-based samples.7,8 In contrast, the TS Broad and CT Broad prevalence estimates (3.2% and 8.6%, respectively), which did not require that tics be chronic, were significantly higher than would be expected based on prior studies; for this reason, only the TS/CT Narrow and Intermediate definitions were included in subsequent analyses.
