The Yale Global Tic Severity Scale: initial testing of a clinician-rated scale of tic severity.

Despite the overt nature of most motor and phonic tic phenomena, the development of valid and reliable scales to rate tic severity has been an elusive goal. The Yale Global Tic Severity Scale (YGTSS) is a new clinical rating instrument that was designed for use in studies of Tourette's syndrome and other tic disorders. The YGTSS provides an evaluation of the number, frequency, intensity, complexity, and interference of motor and phonic symptoms. Data from 105 subjects, aged 5 to 51 years, support the construct, convergent, and discriminant validity of the instrument. These results indicate that the YGTSS is a promising instrument for the assessment of tic severity in children, adolescents and adults.