Rasch analysis of anxiety scales in Parkinson's disease

Objective: Anxiety is a common non-motor symptom in Parkinson's disease (PD). This study analyzed the measurement properties of three frequently used anxiety scales in PD: the Beck Anxiety Inventory (BAI), the Hamilton Anxiety Rating Scale (HARS), and the Hospital Anxiety and Depression Scale-Anxiety subscale (HADS-A). Method: The Rasch model was applied to a multicenter international cohort of 342 patients and assessed the following aspects: fit to the Rasch model, unidimensionality, reliability, response category ordering, item local independence, differential item functioning, and scale targeting. Results: In their original form, the BAI, HARS, and HADS-A, did not fit the Rasch model. A good fit to the Rasch model was only found after significant modifications, including rescoring some items and deleting those failing to fit the model. For the BAI and HADS-A, these adjustments resulted in unidimensionality. The HARS was not unidimensional and separate analyses were performed for its psychic and somatic subscales. Whereas the somatic anxiety subscale fit the Rasch model, this was achieved for the psychic anxiety subscale after modifications. Conclusion: None of the currently used anxiety scales display satisfactory measurement properties for assessing anxiety in PD. The results suggest the need to develop a new disease-specific scale for measuring anxiety in PD.