The validity of instruments measuring tic severity in Tourette's syndrome.

By using four different scales that measure tic severity in Tourette's syndrome, three independent judges concurrently evaluated their validity and interjudge reliability in 20 affected individuals. The Yale Global Tic Severity Scale, Tourette's Syndrome Severity Scale, Tourette's Syndrome-Clinical Global Impression Scale, and the Hopkins Motor and Vocal Tic Scale were equally effective in determining overall severity and showed good interrater reliability. Both historical information and direct observation of the subject were shown to have a significant contribution towards the overall assessment of tic severity. With all instruments, tic symptom ratings were shown to be independent of those for either attention-deficit hyperactivity disorder or obsessive-compulsive disorder. A 67% incidence of behavioral problems and social difficulties was identified by the Child Behavior Checklist. Nevertheless, associations with tic severity were limited to areas showing interference with social relationships and school adjustments. These results extend the understanding of Tourette's syndrome severity scales and provide additional information necessary for the development of a unified rating scale.