Reliability and Validity of the Psoriasis Symptom Inventory in Patients With Psoriatic Arthritis

Objective To evaluate the measurement properties of the Psoriasis Symptom Inventory (PSI) in psoriatic arthritis (PsA). Methods The PSI is an 8‐item, patient‐reported outcome measure of the severity of psoriasis signs and symptoms. This was a secondary analysis of pooled data from a phase II study e...

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Published in:Arthritis care & research (2010) 2015-12, Vol.67 (12), p.1750-1756
Main Authors: Wilson, Hilary D., Mutebi, Alex, Revicki, Dennis A., Mease, Philip J., Genovese, Mark C., Erondu, Ngozi, Nirula, Ajay, Yuan, Feng Jing, Viswanathan, Hema N.
Format: Article
Language:English
Subjects:
Adult
Aged
Antibodies, Monoclonal - therapeutic use
Arthritis, Psoriatic - complications
Arthritis, Psoriatic - diagnosis
Arthritis, Psoriatic - drug therapy
Canada
Clinical Trials, Phase II as Topic
Female
Humans
Male
Middle Aged
Predictive Value of Tests
Psychometrics
Randomized Controlled Trials as Topic
Remission Induction
Reproducibility of Results
Severity of Illness Index
Surveys and Questionnaires
Treatment Outcome
United States
Young Adult
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Summary:Objective To evaluate the measurement properties of the Psoriasis Symptom Inventory (PSI) in psoriatic arthritis (PsA). Methods The PSI is an 8‐item, patient‐reported outcome measure of the severity of psoriasis signs and symptoms. This was a secondary analysis of pooled data from a phase II study evaluating the efficacy of brodalumab in patients with PsA. Unidimensionality and item evaluation were assessed using factor and Rasch analyses. Reliability was assessed using Cronbach's alpha (internal consistency) and intraclass correlation coefficients (ICCs) for PSI scores in patients with stable disease (test–retest). Construct validity was evaluated by correlations between PSI scores and body surface area (BSA) affected by psoriasis and selected Short Form 36 (SF‐36) health survey domains. Known‐groups validity was evaluated based on BSA severity categories, and the ability to detect change was evaluated based on improvement in the subject's global assessment (SGA). Results The analysis sample (n = 154) was 93.5% white and 63.0% female. The mean ± SD baseline affected BSA was 10.4% ± 15.6%, and age was 52.2 ± 11.5 years. The PSI demonstrated unidimensionality, with good item fit and correctly ordered categories, excellent internal consistency (α = 0.95), good test–retest reliability (total score ICC 0.70; item ICCs range 0.67–0.81), convergent validity based on moderate correlations with BSA (r = 0.50), discriminant validity based on small baseline correlations (r 
ISSN:2151-464X
2151-4658
DOI:10.1002/acr.22653