Assessment of the minimum clinically important difference in quality of life in schizophrenia measured by the Quality of Well-Being Scale and disease-specific measures

This study examines the psychometric properties of the Quality of Well Being Scale (QWB), the Positive and Negative Syndrome Scale (PANSS), the Heinrich-Carpenter Quality of Life Scale (QOLS), and the Lenert PANSS-based utility measure in a cohort of patients with schizophrenia and identifies threshold values of clinically meaningful change using the Clinical Global Impressions scale (CGI), as the anchor. The correlation of these measures at baseline and change at 6 and 12 months post enrollment in a comparative effectiveness trial was evaluated in 350 veterans with schizophrenia or schizoaffective disorder. An equipercentile method was used to estimate the minimum clinically important difference (MCID) for each measure. Effect size of 0.30–0.50 for baseline quality of life associated with inpatient status supported concurrent validity. The QWB was moderately correlated with disease-specific measures. The MCID as detected by the CGI at 6 months was 0.17 for QWB, 0.15 for the Lenert utility score, 1.13 for the QOLS, and 20.2 for the PANSS. These differences were stable at 12 months. The QWB is significantly correlated with disease specific measures of health related quality of life in schizophrenia.