Measurement properties and interpretability of the Patient-Reported Impact of Dermatological Diseases (PRIDD) measure.

ABSTRACT

BACKGROUND: Patient-reported outcome measures (PROMs) are crucial for assessing the impact of dermatological conditions on patients' lives, but the existing dermatology-specific PROMs are not recommended for use according to the Consensus-based Standards for the Selection of Health Measurement Instruments (COSMIN). We developed the Patient-Reported Impact of Dermatological Diseases (PRIDD) measure in partnership with patients. It has strong evidence of content validity, structural validity, internal consistency, acceptability, and feasibility. OBJECTIVES: To test PRIDD's remaining measurement properties and establish the interpretability of scores against the COSMIN criteria using classic and modern psychometric methods. METHODS: A global longitudinal study consisting of two online surveys administered two to four weeks apart. Adults (≥ 18 years) living with a dermatological condition were recruited through the International Alliance of Dermatology Patient Organizations' (GlobalSkin) membership network. Participants completed PRIDD, a demographics questionnaire, and other related measures including the Dermatology Life Quality Index (DLQI). We tested PRIDD's criterion validity, construct validity and responsiveness (Spearman's ρ, independent-samples t-tests and ANOVA), test-retest reliability (interclass correlation coefficient [ICC]), measurement error (Smallest Detectable Change or Limits of Agreement [LoA], distribution-based Minimally Important Change [MIC]), floor and ceiling effects (number of minimum and maximum scores and Person-Item Location Distribution Maps), score bandings (κ coefficient of agreement) and anchor-based MIC. RESULTS: 504 patients with 35 dermatological conditions from 38 countries participated. Criterion validity (ρ = 0.79), construct validity (76% hypotheses met), test-retest validity (ICC = 0.93), and measurement error (LoA = 1.3 < MIC = 4.14) were sufficient. Floor and ceiling effects were in the acceptable range (< 15%). Score bandings were determined (κ = 0.47), however, the anchor-based MIC could not be calculated due to an insufficient anchor. CONCLUSIONS: PRIDD is a valid and reliable tool to evaluate the impact of dermatological disease on patients' lives in research and clinical practice. It is the first dermatology-specific PROM to meet the COSMIN criteria. These results support the value of developing and validating PROMs with a patient-centred approach and using classic and modern psychometric methods. Further testing of responsiveness and MIC, cross-cultural translation, linguistic validation, and global data collection are planned.