Psychometric Properties Of The Impact Of Weight On Quality Of Life-Lite (Iwqol-Lite) Questionnaire In A Clinical Trial Sample In Schizophrenia

Background: The IWQOL-Lite has been widely used to assess the impact of weight on quality of life in obese persons. There is evidence demonstrating that IWQOL-Lite is a reliable and valid measure for assessing weight-related quality of life in individuals with schizophrenia or bipolar disorder. Methods: We evaluated the psychometric properties of the IWQOL-Lite using item responses, subscales, and total scores assessed in a randomized, olanzapine-controlled, 12-week, dose-ranging study of ALKS 3831 (olanzapine + samidorphan, a novel mu-opioid antagonist) in subjects with stable schizophrenia (Clinicaltrials.gov, NCT01903837). Results: Of 309 subjects who were randomized in this clinical trial, mean age was 38.8 (SD = 8.4) years, 73.5% were male, and 61.2% were African American. Mean body weight was 77.0 (SD = 13.1) kg and mean body mass index (BMI) was 25.4 (SD = 3.4). At baseline, mean Total score (TS) of IWQOL-Lite was 92.9 (SD = 12.7, range = 26.6–100 with 42.1% at ceiling). Mean subscales for “Physical Function” (PF), “Self-esteem” (SE), “Sexual Life” (SL), “Public Distress” (PD), and “Work” (WK) were 91.8 (SD = 13.7), 91.2 (SD = 18.0), 93.1 (SD = 17.5), 95.6 (SD = 12.2), and 94.9 (SD = 13.8), respectively. The Cronbach’s internal consistency coefficients, α, were0.97 for TS, 0.93 for PF, and 0.92–0.96 for other subscales. TSs were 95.0 (SD = 9.3), 91.6 (SD = 14.6), and 88.1 (SD = 14.8) in baseline BMI groups “<25,” “25–30,” and “>30,” respectively. After controlling for age and gender, statistically significant lower mean TSs were observed for higher BMI groups (F = 3.83, P = .0228) with partial η2 = 0.0247. PF and SE showed similar results. Mean changes in TS from baseline at week 12 were −0.1 (SD = 7.3), −2.2 (SD = 14.2), and −6.4 (SD = 11.2) for subjects with less than 5% increase (including decrease and no change), 5%–10% increase, and >10% increase in BMI, respectively. The standard error of measurement (SEM) was 2.19 for TS, 3.58 for PF, and 3.60 for SE, respectively. Conclusion: The IWQOL-Lite demonstrated excellent internal consistency reliability for weight-related quality of life assessment in schizophrenia within a clinical trial setting. Relationship between IWQOL-Lite scores and BMI was statistically significant, supporting the known-group validity.