Sensitivity Analyses Comparing Time-to-Event Outcomes Only Existing in a Subset Selected Postrandomization and Relaxing Monotonicity
Article first published online: 29 NOV 2010
© 2010, The International Biometric Society
Volume 67, Issue 3, pages 1100–1110, September 2011
How to Cite
Shepherd, B. E., Gilbert, P. B. and Dupont, C. T. (2011), Sensitivity Analyses Comparing Time-to-Event Outcomes Only Existing in a Subset Selected Postrandomization and Relaxing Monotonicity. Biometrics, 67: 1100–1110. doi: 10.1111/j.1541-0420.2010.01508.x
- Issue published online: 14 SEP 2011
- Article first published online: 29 NOV 2010
- Received May 2009. Revised August 2010. Accepted August 2010.
- Causal inference;
- Principal stratification
Summary In randomized studies researchers may be interested in the effect of treatment assignment on a time-to-event outcome that only exists in a subset selected after randomization. For example, in preventative HIV vaccine trials, it is of interest to determine whether randomization to vaccine affects the time from infection diagnosis until initiation of antiretroviral therapy. Earlier work assessed the effect of treatment on outcome among the principal stratum of individuals who would have been selected regardless of treatment assignment. These studies assumed monotonicity, that one of the principal strata was empty (e.g., every person infected in the vaccine arm would have been infected if randomized to placebo). Here, we present a sensitivity analysis approach for relaxing monotonicity with a time-to-event outcome. We also consider scenarios where selection is unknown for some subjects because of noninformative censoring (e.g., infection status k years after randomization is unknown for some because of staggered study entry). We illustrate our method using data from an HIV vaccine trial.