title: Reliability and Validity of the Psoriasis Symptom Inventory in Patients With Psoriatic Arthritis.
abstract: 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 <-0.3) with the SF-36 domains (role-physical, role-emotional, vitality), known groups validity based on significant differences between BSA groups, and responsiveness based on SGA improvements (P < 0.05).
  
  
  CONCLUSIONS
  The PSI demonstrated excellent test-retest and internal consistency reliability and good construct validity in measuring psoriasis signs and symptoms severity in PsA.
authors.affiliation: Evidera, Bethesda, Maryland.
authors.forename: Hilary D
authors.initials: HD
authors.lastname: Wilson
authors.affiliation: Amgen, Thousand Oaks, California.
authors.forename: Alex
authors.initials: A
authors.lastname: Mutebi
authors.affiliation: Evidera, Bethesda, Maryland.
authors.forename: Dennis A
authors.initials: DA
authors.lastname: Revicki
authors.affiliation: Swedish Medical Center and University of Washington, Seattle.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Mease
authors.affiliation: Stanford University, Palo Alto, California.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Genovese
authors.affiliation: Amgen, Thousand Oaks, California.
authors.forename: Ngozi
authors.initials: N
authors.lastname: Erondu
authors.affiliation: Amgen, Thousand Oaks, California.
authors.forename: Ajay
authors.initials: A
authors.lastname: Nirula
authors.affiliation: Amgen, Thousand Oaks, California.
authors.forename: Feng Jing
authors.initials: FJ
authors.lastname: Yuan
authors.affiliation: Amgen, Thousand Oaks, California.
authors.forename: Hema N
authors.initials: HN
authors.lastname: Viswanathan
mesh_terms: D000328:Adult; D000368:Aged; D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D061067:Antibodies, Monoclonal, Humanized; D015535:Arthritis, Psoriatic / Q000150:complications / Q000175:diagnosis* / Q000188:drug therapy; D002170:Canada; D017322:Clinical Trials, Phase II as Topic; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011594:Psychometrics; D016032:Randomized Controlled Trials as Topic; D012074:Remission Induction; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D014481:United States; D055815:Young Adult
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; C571216:brodalumab