OBJECTIVES: The Impact of Weight on Self-Perception Questionnaire (IW-SP) is a 3-item patient-reported outcome instrument measuring the impact of body weight on self-perception. It has been used as an outcome measure in clinical trials for type 2 diabetes (T2D). However, to date, no published data exist on a threshold for meaningful change. The objective of this study was to estimate the minimally important difference (MID) for the IW-SP among people with T2D.

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 MIDs of two conceptually related measures: the Impact of Weight on Quality of Life-Lite Clinical Trials Version (IWQOL Lite CT); and the Ability to Perform Physical Activities of Daily Living (APPADL). Clinically accepted thresholds for percent change in body weight were also used as anchors. Only 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 MID analyses. The analyses were conducted in 2 stages (estimation=2/3 of sample) to derive initial IW-SP MID estimates, and a subsequent confirmation stage (remaining 1/3 of sample).

RESULTS: While the most conceptually related anchors of the IWQOL-Lite-CT Psychosocial scale and two items from that scale performed best in responsiveness analyses, all anchors resulted in a similar estimate of minimal 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 MID estimates. Results were similar across both stages for all analyses.

CONCLUSIONS: The MID for the IW-SP is a 25-point change on the transformed score.