Schizophrenia Quality of Life Scale and Schizophrenia Quality of Life Scale Revision 4: A Systematic Review of Measurement Properties

Background and Hypothesis Schizophrenia is a severe mental disorder that has a significant impact on quality of life (QOL). Measuring QOL can offer insights into treatment efficacy and areas of intervention, highlighting the importance of valid tools assessing QOL in people with schizophrenia.Study Design We employed the COSMIN systematic review guideline to assess the psychometric properties of the schizophrenia quality of life scale (SQLS) and its 4th revision, the schizophrenia quality of life scale revision 4 (SQLS-R4), as patient-reported outcome measures (PROMs).Study Results The search yielded 455 papers, 16 were included, 7 for the SQLS and 9 for the SQLS-R4. Both scales demonstrated good results in risk of bias assessment for internal consistency and convergent validity, the SQLS-R4 additionally for known-groups validity. For the SQLS, PROM development, structural validity, and reliability were suboptimal. The SQLS-R4 showed suboptimality regarding structural validity and reliability and inadequacy for cross-cultural validity and responsiveness. The updated criteria for good measurement properties indicated good convergent validity for the SQLS and good internal consistency, reliability, and convergent validity for the SQLS-R4. The SQLS showed suboptimal results for reliability and known-groups validity, while the SQLS-R4 demonstrated suboptimality in structural validity and known-groups validity. The SQLS had indeterminate structural validity and internal consistency; the SQLS-R4 showed indeterminate responsiveness, and insufficient cross-cultural validity. When using the updated GRADE approach of the COSMIN group, both scales received a very low grade.Conclusions The SQLS and SQLS-R4 hold the potential for recommendation in rating QOL. Identified weaknesses necessitate further validations.