Development and Validation of a Patient-Reported Outcome Measure for Fingernail and Toenail Conditions: The NAIL-Q

Background: Patient-reported outcome measures (PROMs) are needed to measure outcomes that matter to people with nail conditions, from their perspective. Objective: To design a comprehensive new PROM (NAIL-Q) to measure outcomes important in toenail and fingernail conditions. Methods: A mixed methods iterative approach was used. Phase 1 involved concept elicitation interviews that were audio-recorded, transcribed, and coded line-by-line. Concepts were developed into scales and refined through cognitive debriefing interviews with patients and expert input. Data was then collected from an international sample using a crowdsource platform. Eligible participants were aged ≥18 years with a nail condition for at least 3 months. Rasch Measurement Theory (RMT) analysis was used to examine item and scale performance. Other psychometric tests included test-retest reliability, and convergent and construct validity. Results: Phase 1 interviews involved 23 patients with 10 nail conditions and input from 11 dermatologists. The analysis led to the development of 84 items for field-testing. In Phase 2, 555 participants completed the survey. Toenail conditions (n = 441) were more common than fingernail conditions (n = 186). The RMT analysis reduced the number of items tested to 45 in 7 scales measuring nail appearance, health-related quality of life concerns, and treatment outcomes. All items had ordered thresholds and nonsignificant chi-square p values. Reliability statistics with and without extremes for the Person Separation Index were ≥0.79 and Cronbach's alpha were ≥0.83, and for intraclass correlation coefficients were ≥0.81. Construct validity was further supported in that most participants agreed that the NAIL-Q was easy to understand, asked relevant and important questions in a respectful way, and that it should be used to inform clinical care. Conclusion: The NAIL-Q is a rigorously designed and tested PROM that measures nail appearance, health-related quality of life and treatment outcomes. This PROM can be used in clinical practice to inform patient care and to include the patient perspective in research.