A Bifactor and Item Response Theory Analysis of the Eating Disorder Inventory-3

The Eating Disorder Inventory-3 (EDI-3; Garner, 2004) is a 91-item, self-report measure scored on 12 scales (three Eating Disorder Risk scales, nine Psychological scales) and six composites. A sample of 1206 female eating disorder patients was divided randomly into calibration (n = 607) and cross-validation (n = 599) samples for confirmatory factor analyses. A bifactor model best fit the data in both samples, but a model with second-order factors corresponding to the risk and psychological scales approached the fit of the bifactor model. Rasch analysis identified only two items whose level of misfit showed a lack of coherence with other scale items (the only items referring to drug and alcohol use), there were no items with reversed or “disordered” response categories, and only five items had sub-threshold estimated discrimination values. Overall, the results were supportive of the EDI-3’s psychometric properties and consistent with interpretive guidelines presented in the test manual.