title: Propensity score matching and randomization.
abstract: OBJECTIVE
  We used elective total joint replacement (TJR) as a case study to demonstrate selection bias toward offering this procedure to younger and healthier patients.
  
  
  METHODS
  Longitudinal data from 2,202 men were integrated with hospital data and mortality records. Study participants were followed from recruitment (1996-1999) until TJR, death, or 2007 (end of follow-up). A propensity score (PS) was constructed to quantify each subject's likelihood of undergoing TJR. TJR recipients were later matched to their non-TJR counterparts by PS and year of hospitalization. Ten-year mortality from index admission was compared between cases and controls.
  
  
  RESULTS
  Overall, 819 (37.2%) had TJR. Those were younger, healthier, and belonged to higher socioeconomic classes compared with those who were not proposed for surgery. Of the TJR recipients, 718 were matched to 1,109 controls. Cases and controls had similar characteristics and similar years of follow-up from recruitment till index admission. Nonetheless, controls were more likely to die (39.5%) compared with 14.5% in TJR cases (P < 0.001).
  
  
  CONCLUSIONS
  Selection for elective procedures may introduce bias in prognostic features not accounted for by PS matching. Caution must be exercised when long-term outcomes are compared between surgical and nonsurgical groups in a population at risk for that surgical procedure.
authors: School of Allied Health, Faculty of Health Sciences, Australian Catholic University, Level 2, Daniel Mannix Building, 17 Young Street, Fitzroy, Victoria 3065, Australia. Electronic address: george.mnatz@gmail.com.
authors: George
authors: G
authors: Mnatzaganian
authors: Royal Adelaide Hospital, North Terrace, Adelaide, South Australia 5000, Australia.
authors: David C
authors: DC
authors: Davidson
authors: School of Health Sciences, Faculty of Health, Arts and Design, Swinburne University of Technology, John Street, Hawthorn, Victoria 3122, Australia; Discipline of Public Health, School of Population Health, The University of Adelaide, North Terrace, Adelaide, South Australia 5000, Australia.
authors: Janet E
authors: JE
authors: Hiller
authors: Discipline of Public Health, School of Population Health, The University of Adelaide, North Terrace, Adelaide, South Australia 5000, Australia.
authors: Philip
authors: P
authors: Ryan
mesh_terms: D000368:Aged; D063506:Ageism / Q000706:statistics & numerical data; D019644:Arthroplasty, Replacement, Hip / Q000706:statistics & numerical data*; D016022:Case-Control Studies; D015897:Comorbidity; D015986:Confounding Factors, Epidemiologic; D017558:Elective Surgical Procedures / Q000706:statistics & numerical data*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D015207:Osteoarthritis, Hip / Q000628:therapy; D018579:Patient Selection; D011379:Prognosis; D057216:Propensity Score; D011897:Random Allocation; D012307:Risk Factors; D015983:Selection Bias; D012959:Socioeconomic Factors
keywords: Channeling bias; Confounding; Elective total joint arthroplasty; Internal and external validity; Propensity score matching; Randomization; Selection bias