Validation and reliability of the Thai version of the glasgow antipsychotic side-effect scale (GASS) in patients with schizophrenia

Abstract

Objective To examine the validity and reliability of the Thai version of Glasgow Antipsychotic Side-effect Scale (GASS) in patients with schizophrenia. Method A cross-sectional analytical study was conducted among patients aged 20 years and older who had been receiving continuous antipsychotic treatment for at least 3 months and attended Suan Prung Psychiatric Hospital and Maharaj Nakorn Chiang Mai Hospital, Chiang Mai, Thailand. The GASS was translated into Thai using a forward–backward translation process. Psychometric properties were evaluated, including construct validity assessed by confirmatory factor analysis (CFA, n = 72), concurrent validity examined through correlations between GASS scores and the Thai Perceived Stress Scale-10 (T-PSS-10), EQ-5D-5L, and the Pharmacist Medication Adherence Scale (PMAS), as well as reliability assessed by internal consistency and test–retest reliability (n = 53, with a 7-day interval). Results The CFA model demonstrated marginal fit to the empirical data (CFI = 0.919, TLI = 0.909, RMSEA = 0.059, SRMR = 0.141). GASS scores were positively correlated with T-PSS-10 (Spearman’s rho = 0.41) and negatively correlated with EQ-5D-5L utility scores, EQ-5D-5L visual analogue scale scores, and PMAS (Spearman’s rho = −0.64, −0.39, and −0.24, respectively), with statistical significance (p < 0.05). The Thai version of the GASS demonstrated good internal consistency (Cronbach’s alpha = 0.83) and good test–retest reliability (ICC = 0.797, p < 0.05). Conclusion The Thai version of the GASS shows preliminary evidence of acceptable validity and reliability and can be appropriately used to assess antipsychotic side effects in patients with schizophrenia in both clinical practice and research settings.