Document Detail

Quantifying the impact of survivor treatment bias in observational studies.
MedLine Citation:
PMID:  17100859     Owner:  NLM     Status:  MEDLINE    
RATIONALE: Observational cohort studies are frequently used to measure the impact of therapies on the time to a particular outcome. Treatment often has a time-variant nature since it is frequently initiated at varying times during a patient's follow-up. Studies in the medical literature frequently ignore the time-dependent nature of treatment exposure. Survivor treatment bias can arise when the time dependent nature of treatment exposure is ignored since patients who survived to receive treatment may be healthier than patients who died prior to receipt of treatment. AIMS AND OBJECTIVES: The objective of the current study was to explicitly quantify the magnitude of survivor-treatment bias. METHODS: Monte Carlo simulations using parameters obtained from an analysis of patients admitted to hospital with a diagnosis of acute myocardial infarction in Ontario, Canada. RESULTS AND CONCLUSIONS: When the true treatment was null (hazard ratio of 1), estimated treatment effects varied from a 4% reduction in mortality to a reduction in mortality of 27% when the time varying nature of the treatment was ignored. Furthermore, survivor-treatment bias increased as the time required foe exposed patients to receive treatment increased. Similarly, survivor treatment bias was amplified as exposure was defined to be exposure at any time prior to mortality compared to exposure within a fixed time interval starting at the time origin. Ignoring the time-dependent nature of treatment results in overly optimistic estimates of treatment effects. Depending on the period required for patients to initiate therapy, treatments with no effect on survival can appear to be strongly associated with improved survival. The current study is the first to explicitly quantify the magnitude of bias that results from ignoring the time-varying nature of treatment exposure in survival studies.
Peter C Austin; Muhammad M Mamdani; Carl van Walraven; Jack V Tu
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of evaluation in clinical practice     Volume:  12     ISSN:  1356-1294     ISO Abbreviation:  J Eval Clin Pract     Publication Date:  2006 Dec 
Date Detail:
Created Date:  2006-11-14     Completed Date:  2007-02-08     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9609066     Medline TA:  J Eval Clin Pract     Country:  England    
Other Details:
Languages:  eng     Pagination:  601-12     Citation Subset:  IM    
Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada.
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MeSH Terms
Adrenergic beta-Antagonists / therapeutic use*
Cohort Studies
Hydroxymethylglutaryl-CoA Reductase Inhibitors / therapeutic use*
Monte Carlo Method
Myocardial Infarction / drug therapy*,  mortality*
Ontario / epidemiology
Proportional Hazards Models
ROC Curve
Research Design
Selection Bias
Time Factors
Reg. No./Substance:
0/Adrenergic beta-Antagonists; 0/Hydroxymethylglutaryl-CoA Reductase Inhibitors

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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