title: Reliability, validity, and responsiveness of the Impact of Weight on Self-Perceptions Questionnaire (IW-SP) in individuals with type 2 diabetes and obesity.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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).
  
  
  RESULTS
  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<0.001). In the subgroup (n=40) used to estimate responsiveness, weight was significantly less at end point than at baseline (mean, baseline=231.9 vs. end point=222.0 pounds; P<0.001; ES=0.23), and IW-SP scores were significantly better than at baseline (mean, baseline=61.0 vs. end point=72.1 [on a scale of 0-100]; P=0.01; ES=0.34). Mean IW-SP change scores significantly discriminated between those achieving >5% body weight loss and those who achieved <5% (mean change, 23.6 vs. 5.7; P=0.03).
  
  
  CONCLUSIONS
  The IW-SP has demonstrated reliability, validity, and responsiveness in individuals with T2DM and obesity, thereby making it a potentially valuable tool in the evaluation of weight-loss interventions targeted toward patients with T2DM.
authors.affiliation: Global Patient Outcomes and Real World Evidence, Eli Lilly and Company , Indianapolis, Indiana.
authors.forename: Risa P
authors.initials: RP
authors.lastname: Hayes
authors.forename: Amy M
authors.initials: AM
authors.lastname: DeLozier
mesh_terms: D000328:Adult; D015992:Body Mass Index; D001835:Body Weight; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000523:psychology* / Q000628:therapy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000523:psychology* / Q000628:therapy; D011594:Psychometrics / Q000379:methods*; D015203:Reproducibility of Results; D012649:Self Concept; D011795:Surveys and Questionnaires / Q000592:standards*; D014481:United States; D061217:Weight Reduction Programs