Responsiveness and minimal clinically important difference of the Quality of Life Relevance-Acne questionnaire.

INTRODUCTION: Simultaneous international validation of the QOLRELEVANCE-ACNE questionnaire confirmed its convergent validity, internal consistency and test-retest reliability. A grading system of the QOLRELEVANCE-ACNE questionnaire scores was accepted. The objective of the present study was to confirm the responsiveness and establish the Minimally Clinically Important Difference (MCID) for the QOLRELEVANCE-ACNE questionnaire. METHODS: Patients with acne were asked to fill in the QOLRELEVANCE-ACNE and Dermatology Life Quality Index (DLQI) questionnaires. Global acne severity was assessed independently by both dermatologists and patients. Cohen's d, anchor-based approach and the receiver operating characteristic (ROC) curves method were used for confirmation of responsiveness and determination of MCIDs of the QOLRELEVANCE-ACNE questionnaire. RESULTS: The results of 576 acne patients across eight countries (Bulgaria, Croatia, Germany, Greece, Malta, Romania, Spain and Turkey) were analysed. Cohen d was 0.8. Estimated MID was 2.64. The nearest integer above calculated MID is 3. Based on the hypothesis that total scores below MID correspond to no effect on patient's HRQoL, total QOLRELEVANCE-ACNE scores from 0 to 2 correspond to no effect on patient's HRQoL. Correlations coefficient between changes of the QOLRELEVANCE-ACNE scores and changes of the acne severity assessed by the dermatologist and by the patient and changes of the DLQI scores were 0.61, 0.59 and 0.70, respectively. AUCs were excellent (above 0.8). Calculated MCIDs were 3. CONCLUSION: All used methods confirmed excellent responsiveness of the QOLRELEVANCE-ACNE questionnaire. The MCID of 3 for QOLRELEVANCE-ACNE was established. Total QOLRELEVANCE-ACNE scores of 0, 1 and 2 correspond to no effect on patients' life.