Test-retest reliability and measurement error of the Danish WHO-5 Well-being Index in outpatients with epilepsy

The generic questionnaire WHO-5 Well-being Index (WHO-5), which measures the construct of mental well-being has been widely used in several populations across countries. The questionnaire has demonstrated sufficient psychometric properties; however, the test- retest reliability of the WHO-5 scale has yet to be determined. The aim of this study was to evaluate the test-retest reliability and measurement error of the Danish WHO-5 Well-being Index for outpatients with epilepsy. A further aim was to evaluate whether the method of administration (web, paper, or a mixture of the two modalities) influenced the results. Epilepsy outpatients aged ≥15 years from three outpatient clinics in Central Denmark Region were included from August 2016 to April 2017. The participants were randomly divided into four test-retest groups: web-web, paper-paper, web-paper, and paper-web. Test-retest reliability was assessed by intraclass correlation coefficients (ICC) and measurement error by calculating minimal detectable change (MDC) on the basis of the standard error of the measurement. A total of 554 patients completed the questionnaire at two time points. The median duration between test-retest was 22 days. The pooled test-retest reliability estimate was ICC 0.81 (95% CI 0.78; 0.84). The estimated MDC was 23.60 points (95% CI 22.27; 25.10). These estimates showed little variation across administration methods. WHO-5 showed acceptable test-retest reliability in a Danish epilepsy outpatient population across different method of administration; however, the relatively large measurement error should be taken into account when evaluating changes in WHO-5 scores over time. Further research should be done to explore these findings.