The Yale Global Tic Severity Scale (YGTSS) is a tool used to quantify the severity of Tic symptoms in individuals aged 6-17, and is currently one of the most commonly used tools in Tic assessments (Scahill, 2013). The YGTSS is made up of a semi-structured interview, followed by a questionnaire where individuals are asked to rate the severity of their Tic symptoms (both motor and vocal) in domains such as: number, frequency, intensity, complexity, and interference (Leckman et al., 1989). There is also an impairment scale, where the individual rates how the Tic impacts on their daily life and activities (Leckman et al., 1989).
Scoring
When scoring the YGTSS, the tool gives ratings in 5 domains: Total Motor Tic Score, Total Verbal Tic Score, Total Tic Score (Motor + Verbal), Overall Impairment Rating, and Global Severity Score. When calculating the Global Severity score, it is found by adding together the total motor, verbal and impairment scores. The Total Tic Severity Score has a range of 0-50, and the Global Severity Score has a range of 0- 100. A higher score on all scales suggests a more severe Tic, or a greater impact the Tic has on the person’s life.
The tool is therefore designed to measure severity of an individual’s Tic, and not to diagnose or classify an individual’s Tic disorder. In clinical work, the YGTSS may be used to track changes in Tic behavior, or to investigate if a treatment is reducing symptoms (Storch et al., 2011).
Psychometric Properties
Reliability and Validity: Research into the YGTSS has shown that is possessed good convergent and discriminative reliability. Storch et al., compared scores on the YGTSS to other clinical ratings and found there was no significant relations to OCD severity (r .01–.15), parent ratings of externalizing and internalizing behavior (r.07–.20), child ratings of depression (r .02–.26) and anxiety (r .06 –.28)(2013) .
It has also been found to have good inter-rater reliability (Kircanski et al., 2010, Leckman et al., 1989, Storch et al. 2011). Internal consistency was also high, with Cronbach’s alpha reliability coefficients for the Total Motor Tic Score ( .92 and .92), Total Phonic Tic Score (.93 and .93), and Total Tic Score ( .93 and .94) at first and second administrations (Storch et al., 2013).
The YGTSS has been used widely, and has translated versions in Canada (French), Spanish and Polish. The YGTSS can also be administered to the parent and child jointly, to increase reliability of answers and reduce any bias.
Critical Analysis
Strengths: The YGTSS is a short, easy to use tool which asks individuals to reflect on their symptoms over the past 7-10 days, therefore it can also easily be used multiple times over the course of treatment to gauge how the individual is going. The multiple scales and interview used in the YGTSS enables a lot of information to be provided about the severity and interference the Tic symptoms are having on the individual (Storch, 2011).
Weaknesses: The YGTSS has only been used in a child and adolescent population (6-17 years old), its use with individuals over 17 years has not be psychometrically tested. The YGTSS is only a measure of the severity of Tic symptoms, and does not aid clinicians in deciding a treatment response for these symptoms (Storch, 2011). Bias can always play a role in self report measures, such as the YGTSS, and clinicians should be cautious of this.
References
Kircanski, K., Woods, D., Chang, S., Ricketts, E., & Piacentini, J. (2010). Cluster analysis of the Yale Global Tic Severity Scale (YGTSS): Symptom dimensions and clinical correlates in an outpatient youth sample. Journal of Abnormal Child Psychology, 38(6), 777-88.
Leckman, J. F., Riddle, M. A., Hardin, M. T., Ort, S. L., Swartz, K. L., Stevenson, J., et al. (1989). The Yale Global Tic Severity Scale: initial testing of a clinician-rated scale of tic severity. Journal of the American Academy of Child and Adolescent Psychiatry, 28, 566–573.
Scahill, D. (2013). Yale Global Tic Severity Scale. Encyclopedia of Autism Spectrum Disorders. Springer New York. 3415.
Selles, R., Murphy, T., Obregon, D., Storch, E., & Lewin, A. (2013). Treatment decisions for chronic tic disorders. Clinical Practice, 10(6), 765-780.
Storch, E. A., Murphy, T. K., Fernandez, M., Krishnan, M., Geffken, G. R., Kellgren, A. R., & Goodman, W. K. (2007). Factor-analytic study of the Yale Global Tic Severity Scale. Psychiatry research, 149(1), 231-237.
Storch, E., De Nadai, A., Lewin, A., McGuire, J., Jones, A., Mutch, P., Murphy, T. (2011). Defining Treatment Response in Pediatric Tic Disorders: A Signal Detection Analysis of the Yale Global Tic Severity Scale. Journal of Child and Adolescent Psychopharmacology, 21(6), 621-7.
Storch, E. A., Murphy, T. K., Geffken, G. R., Sajid, M., Allen, P., Roberti, J. W., & Goodman, W. K. (2005). Reliability and validity of the Yale Global Tic Severity Scale. Psychological assessment, 17(4), 486.