VIDEOTAPE TIC COUNTS IN THE ASSESSMENT OF TOURETTES-SYNDROME - STABILITY, RELIABILITY, AND VALIDITY

Objective: We examined the short- and long-term temporal stability of tic counts to estimate the minimum length of videotape needed for a re liable index of overall tic activity and determined the interrater rel iability and validity of tic counts based on prolonged videotape segme nts (>10 minutes). Method: Motor and phonic tic counts and clinician r atings were performed on 43 patients with Tourette's syndrome (TS), ag ed 7 to 50 years. Short-term stability was estimated by determining th e mean interval-to-interval correlation of sequential equal-length seg ments from 30-minute videotape recordings of 20 subjects. Long-term st ability was determined by correlating tic counts at 1-week (N = 14) an d 2-week intervals (N = 11). In addition, tic counts were correlated w ith the most widely used clinical ratings of TS. Results: The short-te rm stability data indicated that estimates of motor and phonic tic fre quencies should be based on videotape counts of at least 5 minutes' du ration. Tic counts also were highly reliable and were significantly co rrelated with clinical ratings with the Yale Global Tic Severity Scale and the Clinical Global Impression Scale for Tourette Syndrome. Concl usions: Standardized videotape tic counts can provide highly reliable, stable measures of tic frequencies that are moderately correlated wit h selected global ratings of tic severity.