Validity, reliability, responsiveness and interpretability of the Recap of atopic eczema (RECAP) questionnaire

Background Limited research has been conducted on the measurement properties of the Recap of atopic eczema (RECAP) questionnaire, particularly in relation to interpretability. Objectives To investigate the validity, reliability, responsiveness and interpretability of the Dutch RECAP in adults with atopic dermatitis (AD). Methods We conducted a prospective study in a Dutch tertiary hospital, recruiting adults with AD between June 2021 and December 2022. Patients completed the RECAP questionnaire, reference instruments and anchor questions at the following three timepoints: baseline, after 1-3 days and after 4-12 weeks. Hypotheses testing was used to investigate single-score validity and change-score validity (responsiveness). To assess reliability, both standard error of measurement (SEMagreement) and intraclass correlation coefficient (ICCagreement) were reported. To assess the interpretability of single scores, bands for eczema control were proposed. To investigate the interpretability of change scores, both smallest detectable change (SDC) and minimally important change (MIC) scores were determined. To estimate the MIC scores, four different anchor- based methods were employed: the mean change method, 95% limit cut-off point, receiver operating characteristic curve and predictive modelling. Results In total, 200 participants were included (57.5% male sex, mean age 38.5 years). Of the a priori hypotheses, 82% (single-score validity) and 59% (responsiveness) were confirmed. Known-group analyses showed differences in the RECAP scores between patient groups based on disease severity and impairment of the quality of life. The SEMagreement was 1.17 points and the ICCagreement was 0.988. The final banding was as follows: 0-1 (completely controlled); 2-5 (mostly controlled); 6-11 (moderately controlled); 12-19 (a little controlled); 20- 28 (not at all controlled). Moreover, a single cut-off point of >= 6 was determined to identify patients whose AD is not under control. The SDC was 3.2 points, and the MIC value from the predictive modelling was 3.9 points. Neither floor nor ceiling effects were observed. Conclusions The RECAP has good single-score validity, moderate responsiveness and excellent reliability. This study fills a gap in the interpretability of the RECAP. Our results indicate a threshold of >= 6 points to identify patients whose AD is 'not under control', while an improvement of >= 4 points represents a clinically important change. Given its endorsement by the Harmonising Outcome Measures for Eczema initiatives, the results of this study support the integration of RECAP into both routine clinical practice and research settings.