Rasch analysis of a simplified Beck Depression Inventory

Depression is one of the most clinically relevant mood disorders, and many assessment instruments have been developed to measure it. Probably the most frequently used instrument is Beck’s Depression Inventory (BDI). The simplified BDI (BDI-S) is a more efficient version of the BDI that has been shown to be no less reliable or valid. As the BDI-S has not yet been subjected to rigorous tests of Item Response Theory, it is the aim of the present paper to conduct such an analysis using the Rasch model. This study subjected a simplified version of the BDI consisting of 20 items (BDI-S20) to a Rasch analysis in a sample of N = 5,035 participants. The scale, minus one misfitting item (BDI-S19), yielded a good approximation to Rasch assumptions. Moderate differential item functioning (DIF) was present. It is concluded that the BDI-S19 is an internally valid instrument for assessing depression, although some room for improvement exists.