title: Measurement properties of a patient-reported outcome measure assessing psoriasis severity: The psoriasis symptoms and signs diary.
abstract: BACKGROUND
  Collecting reliable and valid symptom information from patients is critical for assessing psoriasis severity in clinical research.
  
  
  OBJECTIVE
  To evaluate measurement properties of a new patient-reported outcome (PRO), the Psoriasis Symptoms and Signs Diary (PSSD).
  
  
  METHODS
  One hundred six US patients with moderate-to-severe plaque psoriasis completed two versions of the PSSD [a 24-hour recall (PSSD-24h) and 7-day recall (PSSD-7d)] using a 0-10 numerical rating scale. Reliability (test-retest and internal consistency), validity (convergent, divergent and known-groups), responsiveness, and version equivalence were evaluated. Minimally important difference was estimated.
  
  
  RESULTS
  Based on exploratory factor analysis and clinical input, symptom, sign, and total severity scores were established. Internal consistency (Cronbach's alpha ≥ 0.944) and test-retest reliability (intraclass correlation coefficients ≥ 0.824) were acceptable. Correlations with Dermatology Life Quality Index (DLQI) (0.489 to 0.644) indicated convergent validity, while low correlations (< 0.30) with several Short Form (SF)-36 scales indicated divergent validity. PSSD scores differed when patients were categorized by Body Surface Area, DLQI, and Psoriasis Area Severity Index scores. PSSD-24h and PSSD-7d versions were equivalent (Pearson correlations ≥ 0.953).
  
  
  CONCLUSIONS
  PSSD responsiveness should be evaluated in patients receiving treatment.
  
  
  CONCLUSIONS
  The PSSD is reliable and valid in measuring symptoms/signs of patients with moderate-to-severe plaque psoriasis.
authors.affiliation: a Health Outcomes Solutions , Winter Park , FL , USA .
authors.forename: Susan D
authors.initials: SD
authors.lastname: Mathias
authors.affiliation: b Wake Forest University School of Medicine , Winston Salem , NC , USA .
authors.forename: Steven R
authors.initials: SR
authors.lastname: Feldman
authors.affiliation: a Health Outcomes Solutions , Winter Park , FL , USA .|c Neuropsychiatric Research Institute , Fargo , ND , USA .|d University of North Dakota School of Medicine and Health Sciences , Fargo , ND , USA , and.
authors.forename: Ross D
authors.initials: RD
authors.lastname: Crosby
authors.affiliation: a Health Outcomes Solutions , Winter Park , FL , USA .
authors.forename: Hilary H
authors.initials: HH
authors.lastname: Colwell
authors.affiliation: e Janssen Global Services, LLC , Malvern , PA , USA.
authors.forename: Kelly
authors.initials: K
authors.lastname: McQuarrie
authors.affiliation: e Janssen Global Services, LLC , Malvern , PA , USA.
authors.forename: Chenglong
authors.initials: C
authors.lastname: Han
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D000071066:Patient Reported Outcome Measures; D011565:Psoriasis / Q000188:drug therapy; D011594:Psychometrics / Q000379:methods*; D011788:Quality of Life; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires
keywords: Psoriasis; assessment tool; minimal important difference; questionnaire; reliability; validity