title: Calibration of the PROMIS physical function item bank in Dutch patients with rheumatoid arthritis.
abstract: OBJECTIVE
  To calibrate the Dutch-Flemish version of the PROMIS physical function (PF) item bank in patients with rheumatoid arthritis (RA) and to evaluate cross-cultural measurement equivalence with US general population and RA data.
  
  
  METHODS
  Data were collected from RA patients enrolled in the Dutch DREAM registry. An incomplete longitudinal anchored design was used where patients completed all 121 items of the item bank over the course of three waves of data collection. Item responses were fit to a generalized partial credit model adapted for longitudinal data and the item parameters were examined for differential item functioning (DIF) across country, age, and sex.
  
  
  RESULTS
  In total, 690 patients participated in the study at time point 1 (T2, N = 489; T3, N = 311). The item bank could be successfully fitted to a generalized partial credit model, with the number of misfitting items falling within acceptable limits. Seven items demonstrated DIF for sex, while 5 items showed DIF for age in the Dutch RA sample. Twenty-five (20%) items were flagged for cross-cultural DIF compared to the US general population. However, the impact of observed DIF on total physical function estimates was negligible.
  
  
  CONCLUSIONS
  The results of this study showed that the PROMIS PF item bank adequately fit a unidimensional IRT model which provides support for applications that require invariant estimates of physical function, such as computer adaptive testing and targeted short forms. More studies are needed to further investigate the cross-cultural applicability of the US-based PROMIS calibration and standardized metric.
authors.affiliation: Arthritis Center Twente and Psychology, Health & Technology, University of Twente, Enschede, The Netherlands.
authors.forename: Martijn A H
authors.initials: MA
authors.lastname: Oude Voshaar
authors.affiliation: Arthritis Center Twente and Psychology, Health & Technology, University of Twente, Enschede, The Netherlands.
authors.forename: Peter M
authors.initials: PM
authors.lastname: ten Klooster
authors.affiliation: Department of Research Methodology, Measurement and Data Analysis, University of Twente, Enschede, The Netherlands.
authors.forename: Cees A W
authors.initials: CA
authors.lastname: Glas
authors.affiliation: Arthritis Center Twente and Psychology, Health & Technology, University of Twente, Enschede, The Netherlands; Department of Rheumatology and Clinical Immunology, Medisch Spectrum Twente, Enschede, The Netherlands.
authors.forename: Harald E
authors.initials: HE
authors.lastname: Vonkeman
authors.affiliation: Arthritis Center Twente and Psychology, Health & Technology, University of Twente, Enschede, The Netherlands.
authors.forename: Erik
authors.initials: E
authors.lastname: Taal
authors.affiliation: Arthritis, Rheumatism, and Aging Medical Information System Program, Stanford University School of Medicine, Palo Alto, California, United States of America.
authors.forename: Eswar
authors.initials: E
authors.lastname: Krishnan
authors.affiliation: Department of Rheumatology and Clinical Immunology, Ziekenhuisgroep Twente, Almelo, The Netherlands.
authors.forename: Hein J Bernelot
authors.initials: HJ
authors.lastname: Moens
authors.affiliation: Department of Epidemiology and Biostatistics, Vrije Universiteit Medical Center, Amsterdam, The Netherlands.
authors.forename: Maarten
authors.initials: M
authors.lastname: Boers
authors.affiliation: Department of Epidemiology and Biostatistics, Vrije Universiteit Medical Center, Amsterdam, The Netherlands.
authors.forename: Caroline B
authors.initials: CB
authors.lastname: Terwee
authors.affiliation: Department of Rheumatic Diseases, Radboud University Medical Centre, Nijmegen, The Netherlands.
authors.forename: Piet L C M
authors.initials: PL
authors.lastname: van Riel
authors.affiliation: Arthritis Center Twente and Psychology, Health & Technology, University of Twente, Enschede, The Netherlands; Department of Rheumatology and Clinical Immunology, Medisch Spectrum Twente, Enschede, The Netherlands.
authors.forename: Mart A F J
authors.initials: MA
authors.lastname: van de Laar
mesh_terms: D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000503:physiopathology*; D002138:Calibration; D003431:Cross-Cultural Comparison; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D011795:Surveys and Questionnaires; D014481:United States