Conclusion about the association between valve surgery and mortality in an infective endocarditis cohort changed after adjusting for survivor bias.
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.
Tleyjeh
Imad M
IM
Division of Infectious Diseases, Department of Medicine, and Research Center, King Fahd Medical City, Riyadh, Saudi Arabia. tleyjeh.imad@mayo.edu
Ghomrawi
Hassan M K
HM
Steckelberg
James M
JM
Montori
Victor M
VM
Hoskin
Tanya L
TL
Enders
Felicity
F
Huskins
W Charles
WC
Mookadam
Farouk
F
Wilson
Walter R
WR
Zimmerman
Valerie
V
Baddour
Larry M
LM
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