Validity and score interpretation of the 12-item Psoriatic Arthritis Impact of Disease: an analysis of pooled data from two phase 3 trials of bimekizumab in patients with psoriatic arthritis.

Objectives: To investigate psychometric performance of the 12-item Psoriatic Arthritis Impact of Disease (PsAID-12) total and individual item scores in patients with psoriatic arthritis (PsA) and to estimate score change thresholds and scores corresponding to different levels of symptom/impact severity.
Methods: Data up to week 16 from 1252 patients with active PsA enrolled in two randomised controlled trials of bimekizumab (BE OPTIMAL (NCT03895203) and BE COMPLETE (NCT03896581)) were used to assess construct validity (correlations with other patient-reported outcomes), known-groups validity (based on Minimal Disease Activity index, Disease Activity Index for Psoriatic Arthritis and Psoriatic Arthritis Disease Activity Score), reliability (Cronbach's alpha and intraclass correlation coefficients (ICCs)) and responsiveness (sensitivity to change). Clinically meaningful within-patient improvement thresholds were estimated by anchor-based and distribution-based analyses, and symptom/impact severity thresholds were estimated by receiver operating characteristic curve analyses.
Results: The mean (SD) PsAID-12 total score at baseline was 4.19 (1.94). PsAID-12 scores demonstrated good convergent validity and good known-groups validity. Internal consistency reliability (Cronbach's alpha 0.95) and test-retest reliability (ICC ≥ 0.70) were also good. Responsiveness was acceptable (correlations ≥0.30 for most scores). Improvement thresholds were estimated at 1.5-2 points for the PsAID-12 total score and 2 or 3 points for item scores. Thresholds for different levels of symptom/impact severity could be derived for most PsAID-12 items.
Conclusions: The PsAID-12 demonstrated robust psychometric properties in a large sample of patients with active PsA, supporting its use as a fit-for-purpose patient-reported outcome in this population. Furthermore, thresholds for score interpretation were derived.
Competing Interests: Competing interests: LG: Grants from AbbVie, Biogen, Eli Lilly, Novartis, Sandoz and UCB Pharma; consulting fees from AbbVie, Amgen, BMS, Celltrion, Galapagos, Janssen, Eli Lilly, MSD, Novartis, Pfizer, Sandoz and UCB Pharma. A-MO: Research grants to Johns Hopkins University from AbbVie, Amgen and Janssen; consulting fees from BMS, Janssen, Sanofi and UCB Pharma. LCC: Grants/research support from AbbVie, Amgen, Celgene, Eli Lilly, Gilead, Janssen, Novartis, Pfizer and UCB Pharma; consultant for AbbVie, Amgen, BMS, Boehringer Ingelheim, Celgene, Domain, Eli Lilly, Galapagos, Gilead, Janssen, Moonlake Pharma, Novartis, Pfizer, and UCB Pharma; speaking fees from AbbVie, Amgen, Biogen, Celgene, Eli Lilly, Galapagos, Gilead, GSK, Janssen, medac, Novartis, Pfizer, and UCB Pharma. DG: Consultant and/or received grant support from Abbvie, Amgen, BMS, Celgene, Eli Lilly, Gilead, Galapagos, Janssen, Novartis, Pfizer, and UCB Pharma. AO: Grant/research support from AbbVie, Amgen, Janssen, Novartis and Pfizer, consultant of AbbVie, Amgen, BMS, Celgene, CorEvitas, Eli Lilly, GSK, Gilead, Janssen, Novartis, Pfizer, Takeda and UCB Pharma. CGP: Employed by Evidera, a part of Thermo Fisher Scientific, which received funding for this research from UCB Pharma. VC, VT and JL: Employees and stockholders of UCB Pharma. BI: Employee of UCB Pharma; shareholder of AbbVie, GlaxoSmithKline and UCB Pharma. MdW: Over the last five years Stichting Tools has received fees for lectures or consultancy provided by MdW from Celgene, Eli Lilly, Janssen-Cilag, Pfizer and UCB Pharma.
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