Feasibility, acceptability and construct validity of EQ-5D in systemic sclerosis

Abstract

Background: Systemic sclerosis is a chronic disabling disease that is often associated with severe physical and psychological impairment. Nonetheless, health-related quality of life (HRQoL) in patients with systemic sclerosis is often left behind in clinical practice and research. One of the reasons for this lack of evaluation is the current use of tools, such as the short form-36 (SF-36) questionnaire, that are complete but complicated to use in everyday routine. Other self-reported outcome measures such as the health assessment questionnaire (HAQ) are simple, but specifically designed for physical disability.

Study aims and methods: Our aim was to evaluate the feasibility, acceptability and construct validity of EQ-5D, a simple and quick self-assessment tool, and to compare its performance with SF-36 and HAQ. We investigated 119 consecutive patients with systemic sclerosis (94% female; age: median 63 years, interquartile range 53-70 years) at three different rheumatology centres. Acceptability was evaluated from comments made by the patients and feasibility on the basis of the number of patients needing assistance or not answering questions (missing data). Construct validity was based on both convergent and divergent validity between conceptually similar and dissimilar domains, respectively, of the compared instruments.

Results: EQ-5D was well accepted by patients. The percentage of patients missing data in at least one EQ-5D domain was 2.5%. Spearman's correlation coefficients between similar dimensions of EQ-5D vs SF-36 and vs HAQ were moderate (≥0.30) to strong (≥0.50); in contrast, correlation coefficients between less comparable dimensions were weak. As expected, the EQ-5D anxiety/depression domain did not correlate with any of the HAQ domains. The EQ-5D visual analogue scale (VAS) concordance with SF-36 general health domain and HAQ total score was strong (≥0.50 for both). Median value for the EQ-5D index (interquartile range) was 0.81 (0.75-0.86). The EQ-5D index had correlation coefficients >0.40 with all SF-36 domains and with all HAQ domains, HAQ total and HAQ VAS.

Conclusions: Our data demonstrate good acceptability, feasibility and construct validity of EQ-5D in patients with systemic sclerosis. We suggest the use of EQ-5D in systemic sclerosis patients as an HRQoL measure in clinical practice, in randomised clinical trials and/or in pharmacoeconomic evaluations.