Rasch analysis of the hospital anxiety and depression scale in Parkinson's disease.

The hospital anxiety and depression scale (HADS) is commonly used to assess mood in Parkinson's disease (PD) patients. Very few studies analyze the scale from the standpoint of item response theory. This article sought to analyze how the HADS fits the Rasch model in PD. The HADS was administered to 387 PD patients. Three sets of Rasch analyses were performed for the HADS total score, and anxiety and depression subscales (HADS-T, -A, and -D, respectively). Although the HADS-T and HADS-A displayed a good fit, with little threshold disordering and no differential item functioning, the HADS-D failed to fit the model. The person separation index, a reliability measure, was 0.87 (HADS-T) and 0.80 (HADS-A). Both HADS-T and HADS-A showed unidimensionality. Our results supported the use of HADS-T as a measure of psychological distress in PD patients. Moreover, the HADS-A was also an adequate anxiety measure. Further research is required to address the use of HADS-D in PD.