title: The search for stable prognostic models in multiple imputed data sets.
abstract: BACKGROUND
  In prognostic studies model instability and missing data can be troubling factors. Proposed methods for handling these situations are bootstrapping (B) and Multiple imputation (MI). The authors examined the influence of these methods on model composition.
  
  
  METHODS
  Models were constructed using a cohort of 587 patients consulting between January 2001 and January 2003 with a shoulder problem in general practice in the Netherlands (the Dutch Shoulder Study). Outcome measures were persistent shoulder disability and persistent shoulder pain. Potential predictors included socio-demographic variables, characteristics of the pain problem, physical activity and psychosocial factors. Model composition and performance (calibration and discrimination) were assessed for models using a complete case analysis, MI, bootstrapping or both MI and bootstrapping.
  
  
  RESULTS
  Results showed that model composition varied between models as a result of how missing data was handled and that bootstrapping provided additional information on the stability of the selected prognostic model.
  
  
  CONCLUSIONS
  In prognostic modeling missing data needs to be handled by MI and bootstrap model selection is advised in order to provide information on model stability.
authors.affiliation: Institute for Research in Extramural Medicine, VU University Medical Center Amsterdam, The Netherlands. d.vergouw@vumc.nl
authors.forename: David
authors.initials: D
authors.lastname: Vergouw
authors.forename: Martijn W
authors.initials: MW
authors.lastname: Heymans
authors.forename: George M
authors.initials: GM
authors.lastname: Peat
authors.forename: Ton
authors.initials: T
authors.lastname: Kuijpers
authors.forename: Peter R
authors.initials: PR
authors.lastname: Croft
authors.forename: Henrica C W
authors.initials: HC
authors.lastname: de Vet
authors.forename: Henriëtte E
authors.initials: HE
authors.lastname: van der Horst
authors.forename: Daniëlle A W M
authors.initials: DA
authors.lastname: van der Windt
mesh_terms: D000328:Adult; D001530:Belgium; D006302:Health Services Research; D006801:Humans; D007407:Interviews as Topic; D008875:Middle Aged; D010821:Physicians, Family / Q000523:psychology*; D019338:Polypharmacy; D012424:Rural Population; D014505:Urban Population