The development of the S-QoL 18: A shortened quality of life questionnaire for patients with schizophrenia

Objective: The S-QoL 41 is a French self-administered questionnaire that assesses quality of life (QoL) among people with schizophrenia. This study aims to validate a shortened version of the S-QoL for more widespread use in clinical practice. Methods: We used data from four studies conducted in four psychiatric hospitals in France (n = 507). The item reduction and validation processes were based on both item response theory and classical test theory. The final version of the S-QoL was tested for construct validity, reliability, external validity, reproducibility and sensitivity to change. In addition, differential item functioning (DIF) analyses were performed to see whether all items behave in the same way in subgroups divided by age, gender, educational level and clinical form. Results: The S-QoL 18 evaluates eight dimensions: psychological well-being, self-esteem, family relationships, relationships with friends, resilience, physical well-being, autonomy and sentimental life. The factor structure accounted for 78% of the total variance. Internal consistency was satisfactory (item-internal consistency greater than 0.40: Cronbach's alpha coefficients ranged from 0.72 to 0.84). The scalability was satisfactory, with INFIT statistics within an acceptable range. In addition, the results confirmed the absence of DIF and supported the invariance of the item calibrations. Conclusions: The S-QoL 18 is a short self-administered QoL instrument that has a high degree of comparability with S-QoL 41 and presents satisfactory psychometric properties. Future studies should confirm its sensitivity to change. (C) 2010 Elsevier B.V. All rights reserved.