Using Rasch measurement theory to assess three depression scales among adults with epilepsy.

People with chronic conditions, such as epilepsy, are at a high risk for depression; however depression is often under-recognized and undertreated. Depression scales, including one specific to people with epilepsy, have been used for screening in this population, although none have been assessed with Rasch measurement theory. This study used Rasch analyses in order to evaluate and compare the psychometric properties of the modified Beck Depression Inventory, the Patient Health Questionnaire, and the Neurological Disorders Depression Inventory for Epilepsy in a sample of people with epilepsy and depression who participated in an intervention designed to reduce depressive symptoms. A secondary purpose was to assess item functioning across time. The sample includes 44 participants in the Project UPLIFT program who completed the assessments before and after taking part in the intervention. Results of the Rasch analysis indicate that the three depression scales functioned as intended. There was good overall targeting between the items and the sample, acceptable model-data fit, and good reliability of separation for persons, items, and time. The participants experienced a significant decrease in depressive symptoms from pretest to posttest. This study illustrates the value of using model-based measurement with the Rasch model to combine items across the three depression scales. It also demonstrates an approach for analyzing and evaluating the results of small scale intervention programs, such as the UPLIFT program.