Background: Patient-reported outcome measures (PROMs) are crucial in assessing the impact of dermatological conditions on people's lives, but the existing dermatology-specific PROMs are not recommended for use, according to 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 the remaining measurement properties of the PRIDD 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 2-4 weeks apart was carried out. Adults (≥ 18 years of age) living with a dermatological condition were recruited via 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. We tested the 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 the anchor-based MIC of the PRIDD.
Results: In total, 504 people 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 owing to an insufficient anchor.
Conclusions: PRIDD is a valid and reliable tool to evaluate the impact of dermatological disease on people's 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.
Skin conditions are common and can affect a person’s physical, psychological and social wellbeing. Assessing the impact of a skin condition is important, but the current tools do not meet scientific standards. We are a team of dermatologists, health psychologists, researchers and patient leaders from Canada, Germany and the UK. We developed a new tool called the Patient-Reported Impact of Dermatological Diseases (or ‘PRIDD’) to use with adults. To see if a tool is scientifically valid, scientists check its ‘measurement properties’. We already know PRIDD meets most of these. We tested the remaining properties. This included whether PRIDD measures what it should, if its scores are consistent, how accurate it is and if it detects small changes. We also wanted to better understand what PRIDD scores mean. For example, does a score of 20 indicate no, mild, moderate, severe or a very severe impact of a disease? We also wanted to check whether PRIDD can detect very low or high scores (‘floor’ and ‘ceiling’ effects). We wanted to find out the smallest change in scores that patients consider important (known as the ‘minimally important change’). Altogether, 504 people from 38 countries with 35 skin conditions completed PRIDD online. We found that PRIDD met the standards we tested for. We also provided cut-off scores for no, mild, moderate, severe and very severe impact. We could not establish the ‘minimally important change’. PRIDD is the only tool to meet scientific standards that can measure the impact of a skin condition on someone’s life.
© The Author(s) 2024. Published by Oxford University Press on behalf of British Association of Dermatologists.