The minimal important difference of the hospital anxiety and depression scale in patients with chronic obstructive pulmonary disease

Stefan Büchi,Milo A Puhan,Holger J Schünemann,Martin Frey

doi:10.1186/1477-7525-6-46

Abstract

BackgroundInterpretation of the Hospital Anxiety and Depression Scale (HADS), commonly used to assess anxiety and depression in COPD patients, is unclear. Since its minimal important difference has never been established, our aim was to determine it using several approaches.Methods88 COPD patients with FEV1 ≤ 50% predicted completed the HADS and other patient-important outcome measures before and after an inpatient respiratory rehabilitation. For the anchor-based approach we determined the correlation between the HADS and the anchors that have an established minimal important difference (Chronic Respiratory Questionnaire [CRQ] and Feeling Thermometer). If correlations were ≥ 0.5 we performed linear regression analyses to predict the minimal important difference from the anchors. As distribution-based approach we used the Effect Size approach.ResultsBased on CRQ emotional function and mastery domain as well as on total scores, the minimal important difference was 1.41 (95% CI 1.18–1.63) and 1.57 (1.37–1.76) for the HADS anxiety score and 1.68 (1.48–1.87) and 1.60 (1.38–1.82) for the HADS total score. Correlations of the HADS depression score and CRQ domain and Feeling Thermometer scores were < 0.5. Based on the Effect Size approach the MID of the HADS anxiety and depression score was 1.32 and 1.40, respectively.ConclusionThe minimal important difference of the HADS is around 1.5 in COPD patients corresponding to a change from baseline of around 20%. It can be used for the planning and interpretation of trials.

Highlights

Interpretation of the Hospital Anxiety and Depression Scale (HADS), commonly used to assess anxiety and depression in chronic obstructive pulmonary disease (COPD) patients, is unclear
The concept of the minimal important difference the smallest difference in the outcome of interest that informed patients or their proxies perceive as important and that may lead to a change in the management[12], has become the standard approach to interpret the clinical relevance of treatment effects[13,14] For example, the minimal important difference of the Chronic Respiratory Questionnaire (CRQ) has been established to be 0.5 points on the Likert-type scale from 1 to 7[15] Meta-analyses of randomised trials on respiratory rehabilitation show treatment effects between 0.5 and 1.0 on the CRQ exceeding the minimal important difference of 0.5 points and providing a patient-important benefit for a majority of patients.[16]
Study and patients We used the data of a randomized trial that compared different exercise modalities during an inpatient rehabilitation[18] COPD patients with a FEV1 ≤ 50% predicted and German as first or daily language followed an inpatient respiratory rehabilitation with a duration of approximately 3 weeks that included a median number of 13 exercise sessions and that was followed by individually prescribed home-based exercise

Summary

Introduction

Interpretation of the Hospital Anxiety and Depression Scale (HADS), commonly used to assess anxiety and depression in COPD patients, is unclear. It is not a tool to diagnose mood disorders but it has proofed to be a reliable, valid and responsive instrument to assess the severity of symptoms of mood disorders.[10] The self-administration and short completion time makes the HADS an attractive instrument for use in trials. It is, difficult to interpret treatment effects because the minimal important difference of the HADS it is not known[11]. Since a single approach is not sufficient we used anchor- and distribution-based methods to determine the minimal important difference of the HADS.[17]

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