Cross-Ethnic and Cross-National Measurement Invariance of Brief Symptom Inventory-18 In Severe Mental Illness

Background and Purpose: The purpose of this study was to test measurement invariance of the Brief Symptom Inventory-18 (BSI-18, Derogatis, 2000) across three ethnic groups (Euro-American, Latino, and African American) within the United States and across three international urban cultural groups (represented by Los Angeles in United States, Tokyo in Japan and Seoul in Korea) for individuals with severe mental illness. BSI-18 has started to gain a lot of popularity as a measure of psychological distress, mainly for use with the medical and community populations. Even though it is very time efficient and has extensive applicability both as a diagnostic and outcome measure in both research and practice, it needs to be validated across different ethnic and cultural groups to ensure homogeneity of the constructs it is measuring, and for applicability to the severely mentally ill. Method: The present study used secondary data with total sample size of 2,096 mental health consumers with severe mental illness from 3 countries; US (N=1099), Japan (N=784), and Korea (N=213). 18-item version of Brief Symptom Inventory (BSI; Derogatis & Melisaratos, 1983) was used for the analysis. The 3-factor structure of BSI-18 was examined using multiple group CFAs for 5 levels of invariance (configural, metric, scalar, structural and error invariance) within United States and across three nations. Results: The 3-factor model fit well to the data for cross-ethnic sample for all types of invariance: configural (CFI=0.94; RMSEA=0.037), metric (CFI=0.936; RMSEA=0.037), scalar (CFI=0.932; RMSEA=0.036), structural (CFI=0.931; RMSEA=0.037) and measurement error (CFI=0.932; RMSEA=0.036). For the cross-national analysis, the 3-factor model fit well to the data for the configural (CFI=0.937; RMSEA=0.037) and metric invariance (CFI=0.930; RMSEA=0.042). Conclusions and Implications: This is the first study that looked at the cross-ethnic and cross-national invariance of BSI-18 in individuals with severe mental illness. The results confirmed measurement invariance for the cross-ethnic sample within United States for Euro-American, Latino, and African American groups and confirmed BSI-18 as a valid measure of psychological distress in different ethnic groups within United States. The study also established the configural and metric invariance of BSI-18 for the cross-national sample. The BSI-18 can be used as a quick and effective assessment and clinical diagnostic tool. It can also be a bridge between the fields of health and mental health since it already used as a measure of psychological distress in physical health settings.