Psychometric evaluation of the Schizophrenia Quality of Life Scale (SQLS) in English- and Chinese-speaking Asians in Singapore

Objective To assess the psychometric properties of the Schizophrenia Quality of Life Scale (SQLS) in Asians with schizophrenia in Singapore. Methods A consecutive sample of outpatients with schizophrenia completed the English or Chinese version of the SQLS and the Short-Form 36 Health Survey (SF-36) twice during two different clinic visits. The patients were also assessed for presence or absence of 22 psychiatric symptoms. Results About 202 patients (English-speaking: 140) participated in the study. Correlations between SQLS scales and other measures assessing similar constructs ranged from 0.46 to 0.69 (P < 0.001 for all). For SQLS psychosocial and symptoms/side effects scales, item-to-scale correlations were >0.4, Cronbach’s alpha and intra-class correlation coefficient values were close to or exceed 0.7, and Cohen’s effect size, standardized response mean, and Guyatt’s responsiveness index values approximated or exceeded 0.2 for both SQLS language versions; however, for the energy/motivation scale, item-to-scale correlations (range: 0.08–0.51), reliability (range: 0.46–0.66) and responsiveness (range: 0.04–0.08) statistics were not satisfactory for both SQLS versions. Conclusions The SQLS psychosocial and symptoms/side effects scales are valid, reliable and responsive in Singaporean patients with schizophrenia; the appropriateness of energy/motivation scale requires further investigation.