Rasch analysis of the Hospital Anxiety and Depression Scale (HADS) for use in motor neurone disease
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RESEARCH
Open Access
Rasch analysis of the hospital anxiety and depression scale (hads) for use in motor neurone disease Chris J Gibbons1,2*, Roger J Mills1, Everard W Thornton2, John Ealing3, John D Mitchell4†, Pamela J Shaw5, Kevin Talbot6, Alan Tennant7 and Carolyn A Young1
Abstract Background: The Hospital Anxiety and Depression Scale (HADS) is commonly used to assess symptoms of anxiety and depression in motor neurone disease (MND). The measure has never been specifically validated for use within this population, despite questions raised about the scale’s validity. This study seeks to analyse the construct validity of the HADS in MND by fitting its data to the Rasch model. Methods: The scale was administered to 298 patients with MND. Scale assessment included model fit, differential item functioning (DIF), unidimensionality, local dependency and category threshold analysis. Results: Rasch analyses were carried out on the HADS total score as well as depression and anxiety subscales (HADS-T, D and A respectively). After removing one item from both of the seven item scales, it was possible to produce modified HADS-A and HADS-D scales which fit the Rasch model. An 11-item higher-order HADS-T total scale was found to fit the Rasch model following the removal of one further item. Conclusion: Our results suggest that a modified HADS-A and HADS-D are unidimensional, free of DIF and have good fit to the Rasch model in this population. As such they are suitable for use in MND clinics or research. The use of the modified HADS-T as a higher-order measure of psychological distress was supported by our data. Revised cut-off points are given for the modified HADS-A and HADS-D subscales.
Introduction The Hospital Anxiety and Depression Scale (HADS) [1] is a reliable and potentially valid [2,3] measure for detecting depression and anxiety. The scale was designed to exclude measurement of somatic symptoms in medical outpatients; making it potentially suitable for use with motor neurone disease (MND) patients. Due to the scale’s apparent suitability, the HADS has been widely used in MND research for assessing states of anxiety and depression [4-7]. However, questions have been raised as to the suitability of the HADS depression subscale with MND patients as two previous studies [6,7] have omitted item D8 “I feel as though I am slowed down”, on the reasonable assumption that * Correspondence: [email protected] † Contributed equally 1 Walton Centre for Neurology and Neurosurgery, Lower Lane, Liverpool, UK Full list of author information is available at the end of the article
responses to this item would be confounded by physical impairment. Whilst this change had clinical and face validity, in neither study was it accompanied by appropriate statistical or psychometric analysis to justify the alteration. The Rasch model [8], a modern psychometric approach, ensures that the fundamental scaling properties of an instrument are assessed alongside traditional psychometric assessments of reliability and construct validity. The model
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