Patient-reported outcome measures (PROMs) capture patients' perspectives on treatment benefits and harms. Interpreting results of PROMs requires understanding the extent of improvement or deterioration that patients consider important: the minimal important difference (MID), the smallest change in a PROM that patients perceive as an important benefit or harm. No inventory of MIDs for PROMs is currently available, requiring clinicians and researchers to navigate a vast literature to retrieve a specific MID. Even if they find a MID, there is no guidance to ascertain its credibility.
To create an inventory of published anchor-based MIDs associated with PROMs and to determine their credibility.
We searched MEDLINE, Embase, PsycINFO and CINAHL to identify studies estimating anchor-based MIDs of PROMs. Teams of two authors independently screened citations, and identified and extracted relevant data. We collected information on study design, disease or condition, population demographics and characteristics of the PROMs and anchor, and created and applied a new instrument to assess the credibility of MID estimates.
Of 5656 citations retrieved for title and abstract screening, we selected 1716 for full-text screening of which 338 proved eligible. We summarised over 3000 estimates, including MIDs for PROMs across different populations, conditions and interventions, obtained using different anchors and statistical methods. Mean change methods and receiver operating characteristics curve analysis were the most common methods to estimate MIDs. MIDs were largely calculated using patient-reported, as opposed to proxy or clinician-reported anchors. However, most studies failed to report the correlation between the anchor and the PROM; when they did the correlation was lower than 0.5. Thus, credibility of MIDs was often limited.
Our inventory of available MIDs in the medical literature and their associated credibility will be of great use for anyone using PROMs to inform healthcare decisions, including clinical trialists, systematic review authors, patients and clinicians. We will illustrate how our inventory can facilitate the interpretation of results by promoting the use of credible anchor-based MID estimates.
Patient, healthcare consumer involvement:
PROMs and MIDs directly reflect patient opinion.