Using the cumulative common log-odds ratio to identify differential item functioning of rating scale items in the exercise and sport sciences

One aspect of construct validity is the extent to which the measurement properties of a rating scale are invariant across the groups being compared. An increasingly used method for assessing between-group differences in the measurement properties of items of a scale is the framework of differential item functioning (DIF). In this paper we introduce the concept of DIF as a validation tool for scales used in physical education and exercise science, and illustrate the use of the cumulative common log-odds ratio for assessing the presence of DIF with data from the Exercise Imagery Inventory (EII; Giacobbi, Hausenblas, & Penfield, 2005).