Reliability, validity, and responsiveness of the Impact of Weight on Self-Perceptions Questionnaire (IW-SP) in individuals with type 2 diabetes and obesity

The Impact of Weight on Self-Perceptions Questionnaire (IW-SP) assesses an individual's self-perception related to his or her weight. The primary objective of this study was to provide evidence of the reliability, validity, and responsiveness of the IW-SP. Study participants were individuals with type 2 diabetes mellitus (T2DM) and obesity enrolled in clinical weight-loss programs in the United States. Data were obtained for clinical measures, IW-SP, and other patient-reported outcome measures. An intraclass correlation coefficient (ICC) and Cronbach's α were calculated for test-retest reliability and internal consistency, respectively. For validity, correlations and t tests were performed. For responsiveness, baseline and 6-month data for a subgroup of patients were analyzed using the paired t test and calculation of effect size (ES). Reliability data for 106 study participants (mean age, 52 years; 69% female; 31% white; mean body mass index, 38 kg/m(2)) yielded an ICC of 0.85 and Cronbach's α values of >0.89. IW-SP scores were associated with obesity-related quality of life, mental health, and vitality (r>0.50, P