title: Magnitude and consequences of misclassification of incident hip fractures in large cohort studies: the Study of Osteoporotic Fractures and Medicare claims data.
abstract: In the Study of Osteoporotic Fractures (SOF), 18.5 % of incident hip fractures identified in Medicare Fee-for-Service claims data were not reported to or confirmed by the cohort. Cognitive impairment was a modest risk factor for false-negative hip fracture ascertainment via self-report.
  
  
  BACKGROUND
  Prospective cohort studies of fractures that rely on participant self-report to be the initial signal of an incident fracture could be prone to bias if a significant proportion of fractures are not self-reported.
  
  
  METHODS
  We used data from the SOF merged with Medicare Fee-for-Service claims data to estimate the proportion of participants who had an incident hip fracture identified in Medicare claims that was either not self-reported or confirmed (by review of radiographic reports) in SOF.
  
  
  RESULTS
  Between 1/1/1991 and 12/31/2007, 647 SOF participants had a hip fracture identified in Medicare claims, but 120 (18.5 %) were either not reported to or confirmed by the cohort. False-negative hip fracture ascertainment was associated with a reduced modified Mini-Mental State Exam (MMSE) score (odds ratio 1.31 per SD decrease, 95 % C.I. 1.06-1.63). Point estimates of associations of predictors of incident hip fracture were changed minimally when the misclassification of incident hip fracture status was corrected with use of claims data.
  
  
  CONCLUSIONS
  A substantial minority of incident hip fractures were not reported to or confirmed in the SOF. Cognitive impairment was modestly associated with false-negative hip fracture ascertainment. While there was no evidence to suggest that misclassification of incident hip fracture status resulted in biased associations of potential predictors with hip fracture in this study, false-negative incident fracture ascertainment in smaller cohort studies with limited power may increase the risk of type 2 error (not finding significant associations of predictors with incident fractures).
authors.affiliation: Park Nicollet Institute, Minneapolis, MN, USA. schouj@parknicollet.com
authors.forename: J T
authors.initials: JT
authors.lastname: Schousboe
authors.forename: M L
authors.initials: ML
authors.lastname: Paudel
authors.forename: B C
authors.initials: BC
authors.lastname: Taylor
authors.forename: B A
authors.initials: BA
authors.lastname: Virnig
authors.forename: J A
authors.initials: JA
authors.lastname: Cauley
authors.forename: J R
authors.initials: JR
authors.lastname: Curtis
authors.forename: K E
authors.initials: KE
authors.lastname: Ensrud
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density / Q000502:physiology; D003072:Cognition Disorders / Q000523:psychology; D015331:Cohort Studies; D005188:False Negative Reactions; D005260:Female; D005272:Femur Neck / Q000503:physiopathology; D006620:Hip Fractures / Q000145:classification / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology; D006801:Humans; D015994:Incidence; D006278:Medicare / Q000706:statistics & numerical data; D058866:Osteoporotic Fractures / Q000145:classification / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology; D011569:Psychiatric Status Rating Scales; D012307:Risk Factors; D057566:Self Report; D014481:United States / Q000453:epidemiology