Meeting Calendar

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1/24/2025 (virtual seminar)

Time: Friday 1:30-2:45pm 

zoom link:  https://jh.zoom.us/j/95707732172

Speaker:  Krithika Suresh, Research Assistant Professor, University of Michigan at Ann Arbor

Title: Bounded hazard ratio Cox model for the effect of time to treatment on mortality

In resource-limited settings, there is often interest in assessing the effect of time to treatment (TTT) on subsequent mortality. We demonstrate that the traditional Cox proportional hazards model specifying the effect of TTT as a linear term in the log hazard ratio results in a mathematical anomaly that violates the expected monotonic TTT effect on survival (i.e., as TTT increases, survival probability should decrease). Additionally, the quantification of the time to treatment effect from these models is the hazard ratio, which provides an interpretation conditional on surviving until treatment rather than a quantification of the effect of delayed treatment at baseline. We propose a class of bounded hazard ratio (BHR) Cox models that attenuate the hazard ratio for TTT towards the null with increasing treatment time, such that hazard for death after treatment does not exceed the hazard without treatment. Estimation is performed using direct optimization of the partial log-likelihood, and we propose a linearized approximation to fit the model in standard software for large sample sizes. From BHR models, the estimated hazard ratio curve describes how the treatment effect diminishes with delays in treatment. Additionally, we present the marginal survival probability difference comparing immediate treatment to a treatment time in the future. We evaluate the performance of model estimation in a simulation study and demonstrate the use of this approach in an application to treatment for colon cancer using NCDB data. 

Upcoming events

2/7/2025

Guoqing Diao, Professor, Department of Biostatistics and Bioinformatics,The George Washington University (in-person)

2/21/2025

Tianchen Qian, Assistant Professor, Department of Statistics, University of California at Irvine (virtual)

3/7/2025

Jiwei Zhao, University of Wisconsin (virtual)

4/11/2025 

Shouhao Zhou (Penn State): in-person

4/25/2025 

Andrea Arfe (Memorial Sloan Kettering): in-person