A systematic survey identified methodological issues in studies estimating anchor-based minimal important differences in patient-reported outcomes.

Objective: To systematically survey the literature addressing the reporting of studies estimating anchor-based minimal important differences (MIDs) and choice of optimal MIDs.
Study Design and Setting: We searched Medline, Embase and PsycINFO from 1987 to March 2020. Teams of two reviewers independently identified eligible publications and extracted quotations addressing relevant issues for reporting and/or selecting anchor-based MIDs. Using a coding list, we assigned the same code to quotations capturing similar or related issues. For each code, we generated an 'item', i.e., a specific phrase or sentence capturing the underlying concept. When multiple concepts existed under a single code, the team created multiple items for that code. We clustered codes addressing a broader methodological issue into a 'category' and classified items as relevant for reporting, relevant for selecting an anchor-based MID, or both.
Results: We identified 136 eligible publications that provided 6 categories (MID definition, anchors, patient-reported outcome measures, generalizability and statistics) and 24 codes. These codes contained 34 items related to reporting MID studies, of which 29 were also related to selecting MIDs.
Conclusion: The systematic survey identified items related to reporting of anchor-based MID studies and selecting optimal MIDs. These provide a conceptual framework to inform the design of studies related to MIDs, and a basis for developing a reporting standard and a selection approach for MIDs.
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