title: Conclusion about the association between valve surgery and mortality in an infective endocarditis cohort changed after adjusting for survivor bias.
abstract: OBJECTIVE
  Survivor bias commonly weakens observational studies, even those published in premier journals. It occurs because patients who live longer are more likely to receive treatment than those who die early. We sought to quantify the effect of survivor bias on the association between valve surgery and mortality in infective endocarditis (IE).
  
  
  METHODS
  The study cohort included 546 IE patients. We compared the hazard ratios (HR) resulting from two propensity score analysis approaches that adjusted for survivor bias (time-dependent variable and matching on follow-up time) with those achieved using the same models but without that adjustment (time-fixed variable).
  
  
  RESULTS
  In the total cohort, the HR of surgery in the time-dependent model was 1.9 (95% confidence interval [CI] = 1.1-3.2; P = 0.03) vs. 0.9 (95% CI = 0.5-1.4; P = 0.53) in the time-fixed model. In the propensity score-matched subset, the HR of surgery was 1.3 (95% CI = 0.5-3.1; P = 0.56) and 0.8 (95% CI = 0.4-1.7; P = 0.57) in the subset with and without matching on follow-up time, respectively.
  
  
  CONCLUSIONS
  Adjusting for survivor bias changed the conclusion about the association between valve surgery and mortality in IE. Researchers should be aware of this bias when evaluating observational studies of treatment efficacy.
authors.affiliation: Division of Infectious Diseases, Department of Medicine, and Research Center, King Fahd Medical City, Riyadh, Saudi Arabia. tleyjeh.imad@mayo.edu
authors.forename: Imad M
authors.initials: IM
authors.lastname: Tleyjeh
authors.forename: Hassan M K
authors.initials: HM
authors.lastname: Ghomrawi
authors.forename: James M
authors.initials: JM
authors.lastname: Steckelberg
authors.forename: Victor M
authors.initials: VM
authors.lastname: Montori
authors.forename: Tanya L
authors.initials: TL
authors.lastname: Hoskin
authors.forename: Felicity
authors.initials: F
authors.lastname: Enders
authors.forename: W Charles
authors.initials: WC
authors.lastname: Huskins
authors.forename: Farouk
authors.initials: F
authors.lastname: Mookadam
authors.forename: Walter R
authors.initials: WR
authors.lastname: Wilson
authors.forename: Valerie
authors.initials: V
authors.lastname: Zimmerman
authors.forename: Larry M
authors.initials: LM
authors.lastname: Baddour
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015986:Confounding Factors, Epidemiologic; D004696:Endocarditis / Q000401:mortality / Q000601:surgery*; D004812:Epidemiologic Methods; D006349:Heart Valve Diseases / Q000382:microbiology / Q000401:mortality / Q000601:surgery*; D006801:Humans; D008875:Middle Aged; D008910:Minnesota / Q000453:epidemiology; D018579:Patient Selection; D015983:Selection Bias; D017741:Survivors; D013997:Time Factors; D055815:Young Adult