Characterising the potential for recall bias in anchor‐based MCID calculation of patient‐reported outcome measures for chronic rhinosinusitis

OBJECTIVE Anchor-based methods to calculate the minimal clinically important difference (MCID) of a patient-reported outcome measure (PROM) may suffer from recall bias. This has never been investigated for otolaryngic PROMs. We sought to identify evidence of recall bias in calculation of MCIDs of PROMs for patients with chronic rhinosinusitis (CRS). DESIGN Retrospective analysis of data from two previous studies calculating the MCID of the 22-item Sinonasal Outcome Test (SNOT-22) and 5-dimensonal EuroQol questionnaire (EQ-5D) in CRS patients. SETTING Tertiary rhinology clinic. PARTICIPANTS Adults with CRS. MAIN OUTCOME MEASURES SNOT-22 score, and EQ-5D visual analog scale scores (EQ-5D VAS) and health utility values (EQ-5D HUV) before and after medical treatment for CRS. After treatment, participants were asked to rate the change in sinonasal symptoms and general health (the anchor question) as "Much worse," "A little worse," "About the same," "A little better" or "Much better." Participants' responses to the anchor question were checked for association with post-treatment and pre-treatment scores using ordinal regression. RESULTS On univariate association, post-treatment SNOT-22 and EQ-5D scores were associated with respective participants' anchor question responses (P