title: Measuring global physical health in children with cerebral palsy: illustration of a multidimensional bi-factor model and computerized adaptive testing.
abstract: OBJECTIVE
  The purposes of this study were to apply a bi-factor model for the determination of test dimensionality and a multidimensional CAT using computer simulations of real data for the assessment of a new global physical health measure for children with cerebral palsy (CP).
  
  
  METHODS
  Parent respondents of 306 children with cerebral palsy were recruited from four pediatric rehabilitation hospitals and outpatient clinics. We compared confirmatory factor analysis results across four models: (1) one-factor unidimensional; (2) two-factor multidimensional (MIRT); (3) bi-factor MIRT with fixed slopes; and (4) bi-factor MIRT with varied slopes. We tested whether the general and content (fatigue and pain) person score estimates could discriminate across severity and types of CP, and whether score estimates from a simulated CAT were similar to estimates based on the total item bank, and whether they correlated as expected with external measures.
  
  
  RESULTS
  Confirmatory factor analysis suggested separate pain and fatigue sub-factors; all 37 items were retained in the analyses. From the bi-factor MIRT model with fixed slopes, the full item bank scores discriminated across levels of severity and types of CP, and compared favorably to external instruments. CAT scores based on 10- and 15-item versions accurately captured the global physical health scores.
  
  
  CONCLUSIONS
  The bi-factor MIRT CAT application, especially the 10- and 15-item versions, yielded accurate global physical health scores that discriminated across known severity groups and types of CP, and correlated as expected with concurrent measures. The CATs have potential for collecting complex data on the physical health of children with CP in an efficient manner.
authors.affiliation: Health and Disability Research Institute, Boston University School of Public Health, 580 Harrison Ave, Boston, MA, 02218, USA. smhaley@bu.edu
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Haley
authors.forename: Pengsheng
authors.initials: P
authors.lastname: Ni
authors.forename: Helene M
authors.initials: HM
authors.lastname: Dumas
authors.forename: Maria A
authors.initials: MA
authors.lastname: Fragala-Pinkham
authors.forename: Ronald K
authors.initials: RK
authors.lastname: Hambleton
authors.forename: Kathleen
authors.initials: K
authors.lastname: Montpetit
authors.forename: Nathalie
authors.initials: N
authors.lastname: Bilodeau
authors.forename: George E
authors.initials: GE
authors.lastname: Gorton
authors.forename: Kyle
authors.initials: K
authors.lastname: Watson
authors.forename: Carole A
authors.initials: CA
authors.lastname: Tucker
mesh_terms: D000223:Adaptation, Psychological; D000293:Adolescent; D002547:Cerebral Palsy / Q000503:physiopathology*; D002648:Child; D002675:Child, Preschool; D003198:Computer Simulation; D005163:Factor Analysis, Statistical; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008404:Massachusetts; D015233:Models, Statistical; D010414:Pennsylvania; D011795:Surveys and Questionnaires; D055815:Young Adult