title: Item response theory analysis of Centers for Disease Control and Prevention Health-Related Quality of Life (CDC HRQOL) items in adults with arthritis.
abstract: BACKGROUND
  Examine the feasibility of performing an item response theory (IRT) analysis on two of the Centers for Disease Control and Prevention health-related quality of life (CDC HRQOL) modules - the 4-item Healthy Days Core Module (HDCM) and the 5-item Healthy days Symptoms Module (HDSM). Previous principal components analyses confirm that the two scales both assess a mix of mental (CDC-MH) and physical health (CDC-PH). The purpose is to conduct item response theory (IRT) analysis on the CDC-MH and CDC-PH scales separately.
  
  
  METHODS
  2182 patients with self-reported or physician-diagnosed arthritis completed a cross-sectional survey including HDCM and HDSM items. Besides global health, the other 8 items ask the number of days that some statement was true; we chose to recode the data into 8 categories based on observed clustering. The IRT assumptions were assessed using confirmatory factor analysis and the data could be modeled using an unidimensional IRT model. The graded response model was used for IRT analyses and CDC-MH and CDC-PH scales were analyzed separately in flexMIRT.
  
  
  RESULTS
  The IRT parameter estimates for the five-item CDC-PH all appeared reasonable. The three-item CDC-MH did not have reasonable parameter estimates.
  
  
  CONCLUSIONS
  The CDC-PH scale is amenable to IRT analysis but the existing The CDC-MH scale is not. We suggest either using the 4-item Healthy Days Core Module (HDCM) and the 5-item Healthy days Symptoms Module (HDSM) as they currently stand or the CDC-PH scale alone if the primary goal is to measure physical health related HRQOL.
authors.affiliation: Department of Epidemiology, Mailman School of Public Health, Columbia University, 722 West 168th St. Rm 512, New York, NY, 10032, USA. tjm2141@columbia.edu.
authors.forename: Thelma J
authors.initials: TJ
authors.lastname: Mielenz
authors.affiliation: Thurston Arthritis Research Center, School of Medicine, University of North Carolina, Chapel Hill, USA.|Departments of Medicine and Social Medicine, School of Medicine, University of North Carolina, Chapel Hill, USA.
authors.forename: Leigh F
authors.initials: LF
authors.lastname: Callahan
authors.affiliation: Department of Psychology, The Ohio State University, Columbus, OH, USA.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Edwards
mesh_terms: D000328:Adult; D001168:Arthritis / Q000523:psychology*; D002487:Centers for Disease Control and Prevention, U.S.; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology*; D011795:Surveys and Questionnaires; D014481:United States