Evaluating the Power of Food Scale in obese subjects and a general sample of individuals: development and measurement properties

Background: The Power of Food Scale (PFS) was developed to assess the psychological impact of today's food-abundant environments. Objective: To evaluate the structure of the PFS in diverse populations of obese and nonobese individuals. Design: Data were obtained from obese adults in a clinical trial for a weight management drug (n = 1741), and overweight, obese and normal weight adults in a Web-based survey (n = 1275). Exploratory and confirmatory factor analyses were used to investigate the PFS structure using the clinical data. The model developed was then tested using the Web-based data. Relationships between PFS domains and body mass index (BMI) were examined. Logistic regression was used in the Web-based survey to evaluate the association between obesity status and PFS scores. Results: Clinical data indicated that the scale was best represented by a 15-item version with three subscale domains and an aggregate domain (average of three domains); this was confirmed with data from the Web-based survey (Comparative Fit Index: 0.95 and 0.94 for the clinical and Web-based studies, respectively). Cronbach's alpha for both data sets was high, ranging from 0.81 to 0.91. The relationships between BMI and each domain were weak (and approximately linear). A full category increase in PFS domain score (range 1-5) increased the odds of being obese 1.6-2.3 times. Conclusions: The 15-item PFS is best represented by three domains and an aggregate domain. The PFS may provide a useful tool to evaluate the effects of obesity treatments on feelings of being controlled by food in an obesogenic food environment. International Journal of Obesity (2009) 33, 913-922; doi: 10.1038/ijo.2009.107; published online 9 June 2009