Estimating meaningful change for The Impact of Weight on Self-Perception (IW-SP) questionnaire among people with type 2 diabetes

Purpose: The Impact of Weight on Self-perception Questionnaire (IW-SP) is a three-item patient-reported outcome measure (PROM) instrument assessing the impact of body weight on self-perception. To date no published threshold for meaningful change exists. The objective of this study was to estimate the minimal important change (MIC) for the IW-SP among people with type 2 diabetes.

Methods: Responder analyses were conducted using anchor- and distribution-based approaches with existing clinical trial data (SURPASS-2). As SURPASS-2 did not include a priori anchors, a set of alternative exploratory anchors were identified based on the MICs and items from two conceptually related measures used in the trial as well as percent change in body weight. Exploratory anchors with change estimates that were sufficiently related to change in IW-SP (r ≥ 0.30) and were not redundant with other anchors were retained for the MIC analyses. The analyses were conducted in two stages (estimation = 2/3 of sample) to derive initial IW-SP MIC estimates, and a subsequent confirmation stage (remaining 1/3 of sample).

Results: While the most conceptually related anchors and items performed best in responsiveness analyses, all anchors resulted in a similar estimate of minimal meaningful change for the IW-SP total score: a 1-point change in raw units (1-5-point scale), corresponding to a 25-point change for transformed scores (0-100 scale). Distribution-based analyses supported these MIC estimates. Results were similar across both stages for all analyses.

Conclusion: The MIC for the IW-SP for patients with T2D is a 25-point change on the transformed score.