title: Single-factor scoring validation for the Health Assessment Questionnaire-Disability Index (HAQ-DI) in patients with systemic sclerosis and comparison with early rheumatoid arthritis patients.
abstract: OBJECTIVE
  Structural validity for the Health Assessment Questionnaire-Disability Index (HAQ-DI) has recently been provided for patients with rheumatoid arthritis (RA). The goal of the current study was to examine the structural validity of the HAQ-DI in patients with systemic sclerosis (SSc, scleroderma) and to compare its performance with that in patients with RA.
  
  
  METHODS
  The HAQ-DI structural validity was first assessed in a sample of 100 scleroderma patients using confirmatory factor analysis. Second, the similarity of factor structures between SSc patients (n = 291) and RA patients (n = 278) was tested using a multigroup structural validity model to assure that comparison of scores between these two diagnostic groups is appropriate.
  
  
  RESULTS
  Results yielded a single-factor HAQ-DI score which favored the current scoring system of the HAQ-DI (model fit was CFI = 0.99 and RMSEA = 0.04). Moreover, even the most stringent model of multigroup structural validity affirmed the similarity between SSc and RA patients on the HAQ-DI (model fit was CFI = 0.99 and RMSEA = 0.04) nor was it different from a model without any demands on group similarity: CFI difference = 0.007; chi(2) = 4.29, df = 26, p=0.99.
  
  
  CONCLUSIONS
  The current results indicate that a single-factor HAQ-DI is appropriate for future clinical trials in scleroderma and, in addition, HAQ-DI scores among patients with SSc and early RA can be compared legitimately with one another.
authors.affiliation: Consulting Measurement Group, Huntington Beach, CA 91403, USA. jcole@webcmg.com
authors.forename: Jason C
authors.initials: JC
authors.lastname: Cole
authors.forename: Dinesh
authors.initials: D
authors.lastname: Khanna
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Clements
authors.forename: James R
authors.initials: JR
authors.lastname: Seibold
authors.forename: Donald P
authors.initials: DP
authors.lastname: Tashkin
authors.forename: Harold E
authors.initials: HE
authors.lastname: Paulus
authors.forename: Michael R
authors.initials: MR
authors.lastname: Irwin
authors.forename: Sarosh J
authors.initials: SJ
authors.lastname: Motivala
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Furst
mesh_terms: D000203:Activities of Daily Living; D001172:Arthritis, Rheumatoid / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D015337:Multicenter Studies as Topic; D011594:Psychometrics / Q000295:instrumentation*; D016032:Randomized Controlled Trials as Topic; D012595:Scleroderma, Systemic / Q000503:physiopathology*; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires; D014481:United States