Reproducibility and Stationarity for the Schizophrenia Quality of Life Scale Revision 4 (SQLS-R4) on Taiwan PopulationAuthor(s): Chia-Ting Su, Ai-Lun Yang, Chung-Ying Lin
Although the Schizophrenia Quality of Life Scale Revision 4 (SQLS-R4) is a feasible quality of life (QoL) instrument for people with schizophrenia, the reproducibility and stationarity of SQLS-R4 are underdeveloped. The purposes of this study were (1) to examine the reproducibility, including the relative and the absolute reliabilities of the SQLS-R4; (2) to establish the stationarity of the SQLS-R4 through measurement invariance.
One hundred people with schizophrenia filled out the SQLS-R4 twice with an interval of 2 weeks. The relative and absolute reliabilities were examined using intraclass correlation coefficients (ICC), the percentages of standard error of measurement (SEM%), and the smallest real difference (SRD%). The measurement invariance was done through nested models of confirmatory factor analyses.
Both the relative (ICC=0.728 to 0.886) and absolute reliabilities (SEM%=3.13% to 8.47%; SRD%=8.64% to 16.58%) were satisfactory for SQLS-R4, which suggested its adequate stability. The measurement invariance of the three-factor construct of SQLS-R4 remained the same across time for people with schizophrenia. Also, factor loadings (P of Δχ2=0.122), item intercepts (P of Δχ2=0.516), and residual variances of measured items (P of Δχ2=0.370) of SQLS-R4 were partial invariance.
The reproducibility and stationarity were established for SQLS-R4, and the results suggested that the SQLS-R4 is reliable and valid across time. Healthcare professionals can use the SQLS-R4 to longitudinally monitor the QoL of people with schizophrenia. In addition, the SQLS-R4 may be used to measure intervention effects on people with schizophrenia.