The estimation of the minimal important difference (MID) in patient-reported outcomes (PRO) relies on various selection principles and statistical methodologies, resulting in varying degrees of credibility among studies. When applying these findings, it is crucial to consider their evaluation outcomes. In the context of widely accepted MID studies based on the anchoring method, the credibility of the MID of PRO is influenced by the selection of anchors and the statistical methods employed for estimation. Variations in the anchors utilized, differences in clinical trial designs, disparities in the characteristics of measurement subjects and environment, as well as the control of biases in studies, can all contribute to inconsistencies in the MID of PRO. In response to this, McMaster University in Canada has developed a credibility evaluation tool specifically for MID studies in PRO. The tool comprises five core items and four additional items. The five core items encompass an evaluation framework that assesses: (1) Is the patient or necessary proxy responding directly to both the PRO and the anchor? (2) Is the anchor easily understandable and relevant for patients or necessary proxy? (3)Has the anchor shown good correlation with the PRO? (4) Is the MID precise? (5) Does the threshold or difference between groups on the anchor used to estimate the MID reflect a small but important difference? The four additional items concerning transition-rated anchors assess: (1) Is the amount of elapsed time between baseline and follow-up measurement for MID estimation optimal? (2) Does the transition item have a satisfactory correlation with the PRO score at follow-up? (3) Does the transition item correlate with the PRO score at baseline? (4) Is the correlation of the transition item with the PRO change score appreciably greater than the correlation of the transition item with the PRO score at follow-up? Given the relative weights of each item in the tool are uncertain and environment-dependent, items are not scored; instead, an overall judgment is made using a qualitative rating approach. This article introduces the specific items of this tool and illustrates the evaluation process through a case study to improve its use in optimizing PRO results presentation and interpretation in clinical trials, reviews, assessments, and guidelines.
Patient reported outcome measures (PROM) are widely used in clinical research and practice. To aid the interpretation of PROM, researchers have proposed the minimal important difference (MID), the smallest change or difference that patients perceive as important. However, the estimation methods of MID are numerous and inconsistent, which brings difficulties to selecting the optimal MID estimate to interpret PROM results. To address this issue, a research team from McMaster University in Canada has proposed an approach for selecting the optimal MID. This method includes three core steps: evaluating the credibility of MID estimates, assessing the consistency among credible MID estimates, and selecting the optimal value based on contextual factors. The credibility evaluation instrument for anchor-based MID examines five core criteria, including the data sources of PROM and anchor, the interpretability of anchor, the correlation between anchor and PROM, the precision of MID estimates, and the judgment of anchor thresholds. When there are multiple credible MID estimates, the optimal MID estimate is selected by evaluating the consistency among the estimates and considering contextual factors that affect the variability among the estimates, such as the type of intervention, follow-up time, and disease severity. In addition, the team provided recommendations to improve the reporting quality of MID studies. This article provides a detailed introduction and interpretation of these developments, aiming to enhance researchers' and clinicians' understanding and application of MID, thereby supporting clinical research and healthcare decision-making.