Rasch analysis of the hospital anxiety and depression scale in patients with chronic fatigue syndrome

The Hospital Anxiety and Depression Scale (HADS) is widely utilized for assessing psychological distress in medical populations, yet its clinimetric properties in chronic fatigue conditions remain underexplored. Given the complex symptom presentation in chronic fatigue syndrome (CFS), rigorous clinimetric validation is essential for accurate clinical assessment.

This study aimed to evaluate the clinimetric properties of the HADS using Rasch methodology in patients with CFS, with particular emphasis on dimensionality, item functioning, and measurement precision.

Rasch analysis was conducted on HADS responses from 286 participants diagnosed with CFS. The Partial Credit Rasch model was applied to assess overall model fit, item performance, unidimensionality and differential item functioning.

Initial analysis revealed suboptimal model fit, necessitating subtest modifications to address local response dependence. The subtest solution demonstrated acceptable fit to the Rasch model with evidence of strict unidimensionality, high reliability (PSI = 0.87), and no differential item functioning by demographic variables. Rasch-converted interval scores showed improved measurement precision compared to ordinal scoring. Interval scoring yielding a significantly higher mean (M = 22.55, SD = 3.78) compared to unconverted scoring (M = 20.30, SD = 6.87), t(275) = -19.54, p < .001, indicating that ordinal scoring systematically underestimates the latent trait level. Interval scores showed a 45 % reduction in measurement error demonstrated by the substantial reduction in standard error.

The HADS demonstrated acceptable measurement properties in patients with CFS. The development of ordinal-to-interval conversion tables enhances the scale's precision, supporting its continued use in clinical and research contexts.