Rasch analysis of the dimensional structure of the Hospital Anxiety and Depression Scale.

The Hospital Anxiety and Depression Scale (HADS) has been used extensively in cancer patients to identify psychological distress. Reports of the factor structure and screening performance of the instrument vary. Rasch models allow an assessment of the structure of a questionnaire by identifying item fit. Removal of misfitting items may improve both the dimensionality and efficacy of screening questionnaires. A Rasch analysis of the HADS-T and subscales was used to explore the factor structure, dimensionality and screening efficacy. A total of 1855 patients completed a touchscreen version of the HADS, including 381 patients who had received a psychiatric interview (SCAN/PSE). These data were analysed using Rasch models, and the screening efficacy at identifying cases of psychological distress and anxiety and depression evaluated. The results demonstrated that the structure of the HADS-T and subscales was unidimensional. Three items from the HADS-T, and one from each of the subscales demonstrated misfit. Screening efficacy for the HADS-T and subscales was modest. However, removal of misfitting items had little impact on screening, demonstrating that items could potentially be omitted, if required. The item range covered a narrow spectrum of psychological distress, predominantly higher levels of distress. Additional items have to be added if screening for moderate to mild distress is to be improved for cancer patients.