Determining the minimal important change of the recap of atopic eczema (RECAP) instrument in clinical trials

Background The Recap of atopic eczema (RECAP) is a patient‐reported instrument designed to assess eczema control. There is a lack of evidence on the interpretability of change scores in clinical trials. Objectives To calculate the smallest detectable change (SDC) in RECAP and estimate the minimal important change (MIC) for RECAP using various calculation methods in three eczema clinical trial datasets. Methods In this study, four anchor‐based methods (within‐person score change, between‐patient score change, predictive modelling, receiver operating characteristic curve) and a distribution‐based method (effect size) was used to determine the MIC of RECAP. The trial datasets involved children (0–12 years), young people (13–25 years) and adults (>25 years) with all eczema severities. Results A total of 698 participants were included in this study. The SDC was between 1.74 and 1.80. For the anchor‐based methods, the patient global assessment anchor provided MIC values ranging from 2.35 to 3.94 and the patient oriented eczema measure anchor yielded values between 1.11 and 3.62. The MIC for the distribution‐based method ranged from 2.66 to 3.06, respectively. Conclusions The interpretability of RECAP was improved by establishing MIC values and the following thresholds are suggested for interpreting changes in RECAP scores: