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An extension MID credibility item addressing construct proximity is a reliable alternative to correlation item

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      To extend the anchor-based minimal important differences (MIDs) credibility instrument by adding an item addressing construct proximity as the alternative to the correlation item.

      Study design and Setting

      The credibility instrument includes one core items addressing the correlation between the patient-reported outcome measure (PROM) and the anchor. However, the majority of MID studies in the literature fail to report the correlation. As an alternative item, we added a subjective assessment of similarity of the constructs (i.e., construct proximity) between the PROM and anchor and generated principles for the assessment. We sampled 101 MIDs and analyzed the assessments performed by each pair of raters. By calculating weighted Cohen’s kappa, we assessed the reliability of the assessments.


      Construct proximity assessment is based on the anticipated association between the anchor and PROM constructs: the closer the anticipated association, the higher the rating. Our detailed principles address the most frequently used anchors: transition ratings, measures of satisfaction, other PROMs, and clinical measures. The assessments showed acceptable agreement (weighted kappa 0.74, 95% CI 0.55 to 0.94) between raters.


      In the absence of a reported correlation coefficient, construct proximity assessment provides a useful alternative in the credibility assessment of anchor-based MID estimates.


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