Aim: The aim of the study is to analyse the psychometric properties of the Spanish version of the Yale Global Tics Severity Scale (YGTSS). In addition, we analysed the sensitivity of this Scale for measuring change, as an instrument for quantifying the clinical evolution of patients with Tourette syndrome.
Patients and methods: Analysis of the properties of the adapted version of the YGTSS questionnaire is focused on the validity of the concept (principal component factor analysis), internal consistency (Cronbach's alpha), intra-observer reliability (intraclass correlation coefficient) and sensitivity to change (Wilcoxon rank sum test).
Results: The factor analysis confirmed the existence of two dimensions on the scale, which account for 76.3% of the variability. The internal consistency, measured by Cronbach's alpha, was 0.997 for the motor tic dimension and 0.996 for the phonic tic dimension. The intra-observer reliability, assessed by intraclass correlation coefficient, was equal to or greater than 0.95, both for the 10 items related to tics (motor and phonic) and for the item related to disability. In the global scores for motor tics, phonic tics and disability, there were statistically significant differences between the mean score for the first interview (incorporation into the study group) and the second one (after 15 days' treatment).
Conclusions: The Spanish version of the YGTSS adequately reflects the three psychometric properties examined in our study population. Its validity and reliability is greater in the motor and phonic tic dimensions than in that of disability.