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: <2.0 points is possibly a measurement error; 2.0-2.9 points denotes a small improvement that may be clinically relevant; 3.0-3.9 points indicates an improvement that is likely to be clinically important and ≥4.0 points is highly likely to represent a clinically important change.