Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2012 Jan;15(1):167-74.
doi: 10.1016/j.jval.2011.07.010. Epub 2011 Oct 1.

Extension of Kaplan-Meier methods in observational studies with time-varying treatment

Stanley Xu  1 , Susan Shetterly, David Powers, Marsha A Raebel, Thomas T Tsai, P Michael Ho, David Magid
Affiliations

Extension of Kaplan-Meier methods in observational studies with time-varying treatment

Stanley Xu et al. Value Health. 2012 Jan.

Abstract

Objectives: Inverse probability of treatment weighted Kaplan-Meier estimates have been developed to compare two treatments in the presence of confounders in observational studies. Recently, stabilized weights were developed to reduce the influence of extreme inverse probability of treatment-weighted weights in estimating treatment effects. The objective of this research was to use adjusted Kaplan-Meier estimates and modified log-rank and Wilcoxon tests to examine the effect of a treatment that varies over time in an observational study.

Methods: We proposed stabilized weight adjusted Kaplan-Meier estimates and modified log-rank and Wilcoxon tests when the treatment was time-varying over the follow-up period. We applied these new methods in examining the effect of an anti-platelet agent, clopidogrel, on subsequent events, including bleeding, myocardial infarction, and death after a drug-eluting stent was implanted into a coronary artery. In this population, clopidogrel use may change over time based on a patient's behavior (e.g., nonadherence) and physicians' recommendations (e.g., end of duration of therapy). Consequently, clopidogrel use was treated as a time-varying variable.

Results: We demonstrate that 1) the sample sizes at three chosen time points are almost identical in the original and weighted datasets; and 2) the covariates between patients on and off clopidogrel were well balanced after stabilized weights were applied to the original samples.

Conclusions: The stabilized weight-adjusted Kaplan-Meier estimates and modified log-rank and Wilcoxon tests are useful in presenting and comparing survival functions for time-varying treatments in observational studies while adjusting for known confounders.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Crude Kaplan-Meier curves for bleeding, MI, and death.
Figure 2
Figure 2
Stabilized weight adjusted Kaplan-Meier curves for bleeding, MI, and death.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Kaplan EL, Meier P. Nonparametric estimation from incomplete observations. J Am Stat Assoc. 1958;53:457–81.
    1. Cox DR. Regression Models and Life Tables. J R Stat Soc Series B. 1972;34:187–220.
    1. Hosmer DW, Lemeshow S. Regression modeling of time to event data. John Wiley & Sons; New York: 1999. Applied survival analysis.
    1. Rosenbaum PR, Rubin DB. The central role of the propensity score in observational studies for causal effects. Biometrika. 1983;70:41–55.
    1. Rosenbaum PR, Rubin DB. Reducing bias in observational studies using subclassification on the propensity score. J Am Stat Assoc. 1984;79:516–24.

MeSH terms