Yale Global Tic Severity Scale (YGTSS)

Abstract

The Yale Global Tic Severity Scale (YGTSS) is a widely recognized and frequently utilized clinical instrument designed to quantify the severity and associated impairment of tic symptoms in children and adolescents, typically aged 6 to 17 years. Developed by Leckman et al. (1989), the YGTSS is currently one of the most common tools employed in tic assessments (Scahill, 2013).

The scale utilizes a semi-structured interview followed by a questionnaire to rate the severity of both motor and vocal tics across key domains, including number, frequency, intensity, complexity, and interference. Furthermore, the YGTSS includes an Impairment Scale to gauge the impact of the tics on the individual’s daily life and activities. The instrument is intended to measure severity and track changes in symptoms, serving as a vital tool for evaluating treatment efficacy, rather than providing an initial diagnosis of a tic disorder.

Keywords

Yale Global Tic Severity Scale, YGTSS, Tic symptoms, Motor tics, Vocal tics, Severity scale, Child assessment, Adolescent psychiatry, Tic disorder, Psychometrics

Authors

James F. Leckman, Mark A. Riddle, Margaret T. Hardin, Steven L. Ort, Kevin L. Swartz, Jeffrey Stevenson, et al.

Purpose

The primary purpose of the Yale Global Tic Severity Scale (YGTSS) is to provide clinicians and researchers with a standardized, quantitative measure of the severity of current and recent tic symptoms. This quantification allows for consistent baseline assessments and reliable tracking of symptom fluctuation over time, particularly in response to pharmacological or behavioral interventions (Storch et al., 2011).

The scale is structured not only to assess the physical manifestation of motor and verbal tics but also to measure the overall functional impairment that these symptoms impose on the individual’s daily life, thereby offering a holistic perspective on the disorder’s impact. The YGTSS is designed strictly for measuring severity, not for diagnostic classification.

Construct

The YGTSS measures the psychological and behavioral construct of Tic Severity and Associated Impairment. This construct is broken down into two main components: Tic Symptom Severity and Global Impairment. The Symptom Severity component evaluates the quantitative and qualitative aspects of tics across five specific domains: number of different tics, frequency of tics, intensity of tics, complexity of tics, and interference caused by tics (Leckman et al., 1989).

The Global Impairment Rating, which forms a crucial part of the final score, assesses the extent to which the total tic symptomatology affects the individual’s academic, social, and familial functioning, thus providing a measure of the burden of the tic disorder on daily activities. The scoring system yields Total Motor Tic, Total Verbal Tic, Total Tic (Motor + Verbal), Overall Impairment, and a comprehensive Global Severity Score.

Validity

Research into the YGTSS has demonstrated that it possesses good convergent validity, correlating well with other established clinical ratings of tic severity. Furthermore, the instrument exhibits strong discriminative reliability, successfully distinguishing tic severity from other co-occurring psychological conditions often seen in this population.

A study by Storch et al. (2013) supports this discriminative capacity, showing no significant relations between YGTSS scores and the severity of Obsessive-Compulsive Disorder (OCD) (r .01–.15), parent ratings of externalizing and internalizing behavior (r.07–.20), or child ratings of depression (r .02–.26) and anxiety (r .06 –.28). This evidence confirms that the YGTSS is specifically measuring tic phenomena rather than general psychopathology.

Reliability

The YGTSS is noted for its high degree of reliability, a critical psychometric property in clinical settings. Multiple studies have confirmed its robust inter-rater reliability, indicating that different clinicians administering and scoring the scale independently arrive at highly similar results (Kircanski et al., 2010; Leckman et al., 1989; Storch et al., 2011). This consistency is vital for multi-site clinical trials and longitudinal studies.

Internal consistency, measured by Cronbach’s alpha, is also reported as consistently high across various subscales. Storch et al. (2013) reported coefficients for the Total Motor Tic Score (α = .92 and .92), Total Phonic (Vocal) Tic Score (α = .93 and .93), and the combined Total Tic Score (α = .93 and .94) across initial and subsequent administrations, confirming the strong internal coherence of the instrument.

Factor Analysis

A factor-analytic study of the YGTSS was conducted by Storch et al. (2007) to determine the underlying structure of the scale. This research generally supports the conceptual division of the scale into distinct factors corresponding to Motor Tic Severity and Vocal Tic Severity, alongside the separate Impairment Rating.

The findings reinforce the scale’s utility in providing separable scores for motor and vocal symptoms, ensuring that the clinical evaluation accurately reflects the specific symptom dimensions experienced by the individual. This factor structure is crucial for defining treatment response in pediatric populations, as demonstrated in subsequent signal detection analyses (Storch et al., 2011).

Instrument

Test Type: Clinician-rated scale combined with a semi-structured interview.

Format: Semi-structured interview followed by a questionnaire/rating section. Individuals reflect on symptoms over the past 7–10 days. The scale can be administered jointly to the child and parent to reduce bias and increase reliability.

Language Available: English, French (Canadian version), Spanish, and Polish.

Population Group: Clinical and research populations presenting with tic symptoms or chronic tic disorders.

Age Group: Children and Adolescents (6–17 years old).

Population Details: The YGTSS is specifically validated for the child and adolescent population. Its psychometric properties have not been formally tested or validated for use in individuals aged 18 years or older.

Test Methodology: Administration involves rating tics across domains for both motor and vocal types. The Total Tic Severity Score ranges from 0–50, and the Global Severity Score (which includes the impairment rating) ranges from 0–100. Higher scores indicate more severe symptoms.

Keywords

Scoring, Impairment rating, Inter-rater reliability, Cronbach’s alpha, Treatment efficacy, Child psychology, YGTSS, Vocal tics, Motor tics

Authors

Author ORCID Identifier: Information not provided in source content.

Affiliation Email addresses: Information not provided in source content.

Correspondence Address: Information not provided in source content.

Permissions & Fee and Test Year

Test Year: Initial validation and testing was completed in 1989 (Leckman et al.).

Permissions and Fees: The YGTSS is a standardized academic instrument widely used in clinical and research settings. Specific permissions for reproduction or commercial use should be directed to the primary authors or Yale University, as applicable.

Reference’s

The following academic sources were used in the development and validation of the YGTSS:

• 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.

Items of the Yale Global Tic Severity Scale (YGTSS)

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

The YGTSS assesses the severity of tic symptoms (both motor and vocal) across the following domains:

• Number
• Frequency
• Intensity
• Complexity
• Interference

Additionally, the scale includes an Impairment Scale where the individual rates the impact of the Tic on their daily life and activities.