Obesity researchers have a growing interest in measuring the impact of weight and weight reduction on quality of life. The Impact of Weight on Quality of Life questionnaire (IWQOL) was the first self-report instrument specifically developed to assess the effect of obesity on quality of life. Although the IWQOL has demonstrated excellent psychometric properties, its length (74 items) makes it somewhat cumbersome as an outcome measure in clinical research. This report describes the development of a 31-item version of the IWQOL (IWQOL-Lite). IWQOLs from 996 obese patients and controls were used to develop the IWQOL-Lite. Psychometric properties of the IWQOL-Lite were examined in a separate cross-validation sample of 991 patients and controls. Confirmatory factor analysis provided strong support for the adequacy of the scale structure. The five identified scales of the IWQOL-Lite (Physical Function, Self-Esteem, Sexual Life, Public Distress, and Work) and the total IWQOL-Lite score demonstrated excellent psychometric properties. The reliability of the IWQOL-Lite scales ranged from 0.90 to 0.94 and was 0.96 for the total score. Correlations between the IWQOL-Lite and collateral measures supported the construct validity of the IWQOL-Lite. Changes in IWQOL-Lite scales over time correlated significantly with changes in weight, supporting its sensitivity to change. Significant differences in IWQOL-Lite scale and total scores were found among groups differing in body mass index, supporting the utility of the IWQOL-Lite across the body mass index spectrum. The IWQOL-Lite appears to be a psychometrically sound and clinically sensitive brief measure of quality of life in obese persons.
