title: Multidimensional item response theory models yielded good fit and reliable scores for the Short Form-12 questionnaire.
abstract: OBJECTIVE
  To propose a multidimensional item response theory (MIRT) scoring system for the Short Form 12 (SF-12) with good psychometric properties in terms of fit and reliability.
  
  
  METHODS
  Two models, indicating physical (PCS) and mental component summary (MCS) dimensions, were fitted to SF-12 data from the European Study of the Epidemiology of Mental Disorders, a representative sample from European adult general population (n=21,425; response rate=61.2%). Goodness of fit, information, reliability, and agreement of individual scores were compared with the classical SF-12 and RAND-12 algorithms.
  
  
  RESULTS
  The bidimensional response process (BRP) model, where all items are indicators of both dimensions, yielded the best fit (root mean square error of approximation=0.057, comparative fit index=0.95, and Tucker-Lewis index=0.94), and highly agreed with PCS and MCS scores from the SF-12 (intraclass correlation coefficients of 0.92 and 0.88, respectively) and RAND-12 (0.88 and 0.95). Regarding reliability, the BRP yielded 0.75 and 0.77 (PCS and MCS, respectively), greater than SF-12 (0.65 and 0.66) and RAND-12 (0.65 and 0.67). As indicated by scale linking, MIRT scores can be interpreted similarly to the classical scores.
  
  
  CONCLUSIONS
  The MIRT models showed a clear construct structure for the PCS and MCS dimensions, defined by functional and role limitation content. Results support the use of SF-12 MIRT-based scores as a valid and reliable option to assess health status.
authors.affiliation: Health Services Research Unit, IMIM-Institut Hospital del Mar d'Investigacions Mèdiques, Doctor Aiguader 88, E-08003 Barcelona, Spain.
authors.forename: Carlos G
authors.initials: CG
authors.lastname: Forero
authors.forename: Gemma
authors.initials: G
authors.lastname: Vilagut
authors.forename: Nuria D
authors.initials: ND
authors.lastname: Adroher
authors.forename: Jordi
authors.initials: J
authors.lastname: Alonso
mesh_terms: D006304:Health Status; D006801:Humans; D001523:Mental Disorders / Q000175:diagnosis*; D011594:Psychometrics; D015203:Reproducibility of Results; D012494:Sampling Studies; D011795:Surveys and Questionnaires / Q000592:standards*