Background: The ability to interpret and, consequently, include patient-reported outcomes (PROs) in the decision-making process along with other patient-important outcomes relies on the understanding of what improvement or reduction in the PRO represents a change that is important to patients. With such understanding, treatment effects can be understood in terms of their magnitude as large, moderate, small but still important, or negligible. The most common reference point for the interpretation of PROs is the minimal important difference (MID), which provides a measure of the smallest change in a PRO that patients would perceive as an important benefit or harm. Although MIDs are available for many PROs, users of these MIDs have no guidance on how to determine how credible these estimates are.
Objective: To develop an instrument to measure the credibility of MIDs estimates studies.
Methods: We are currently conducting a systematic survey that summarizes and appraises available methods to estimate anchor-based MIDs. We searched MEDLINE, EMBASE, PsycINFO, and CINAHL (1989 to present) to identify studies addressing methods to estimate anchor-based MIDs of PRO instruments or reporting empirical ascertainment of anchor-based MIDs. Teams of two reviewers will independently screen the citations identified, and extract relevant data. We will summarize the available methods and develop a new instrument addressing the credibility of empirically ascertained MIDs. We will user-test and pilot our tool, and assess its inter-rater reliability.
Discussion: Our new instrument will allow users to determine the extent to which the design and conduct of studies measuring MIDs is likely to have protected against misleading estimates. In addition, researchers interested in generating these estimates can learn about key aspects that need to be considered in MID study designs to minimize bias. We will present the methods and final draft of the instrument.