The EuroQol five-dimensional questionnaire (EQ-5D) is a generic preference-based measure of health-related quality of life, and several studies have made attempts to estimate the minimally important difference (MID) for the EQ-5D index score.
To estimate the MID of the five-level EQ-5D (EQ-5D-5L) index score in a population-based sample of adults with type 2 diabetes and to explore whether the MID estimate varies by baseline index score and the direction of change in health status.
We used longitudinal survey data of adults with type 2 diabetes in Alberta, Canada. The EQ-5D-5L MID was estimated first by the instrument-defined approach, which used the difference between the baseline index scores and the index scores of simulated single-level transitions, and then by the anchor-based approach, which categorized 1-year changes in depressive symptoms, diabetes-related distress, as well as physical and mental health functioning into no change, small change, and large change groups, wherein the MID was estimated as the average change in index score of the small change group.
Using the instrument-defined approach, MID estimates were 0.043, 0.040, and 0.045, whereas anchor-based MID estimates were 0.042, 0.034, and 0.049 for all change, improvement, and deterioration, respectively. Larger MID estimates were observed for lower baseline index scores and for deterioration in health status.
MID estimates of the EQ-5D-5L index score were consistent between instrument-defined and anchor-based approaches and ranged between 0.03 and 0.05. Estimates varied by baseline index score and the direction of change, with similar results for patient subgroups.