yale global tic severity scale yale global tic severity scale the yale global tic severity scale (ygtss) is a psychological measure designed to assess the severity and frequency of symptoms of disorders such as tic disorder, tourette syndrome, and obsessive-compulsive disorder, in children and adolescents between ages 6 and 17. yale global tic severity scalepurposeassess tics part of a series onpsychology outline history subfields basic types abnormal behavioral behavioral genetics biological cognitive/cognitivism comparative cross-cultural cultural developmental differential evolutionary experimental mathematical neuropsychology personality positive psychodynamic psychometrics quantitative social applied psychology applied behavior analysis clinical community consumer counseling critical educational environmental ergonomics food forensic health humanistic industrial and organizational legal medical military music occupational health political psychometrics religion school sport traffic lists disciplines organizations psychologists psychotherapies research methods theories timeline topics psychology portal the questionnaire is divided into three parts over the span of 17 pages: one section identifies symptoms of motor and phonic tics, severity, and age of onset. another section concerns ocd symptoms, severity, and age of onset, and the last section concerns environmental effects on symptoms. the ygtss is completed by the parent and takes approximately 15–20 minutes. the questionnaire has shown good reliability and validity in assessing tic severity in recent studies.