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Journals / Gazi University Journal of Science / 2025 / Volume: 38 Issue: 4

The Comparison of Time Functions in the Extended Cox Regression Model

Hatice Işık(HACETTEPE UNIVERSITY)0000-0002-5342-7708
Nihal Ata Tutkun(HACETTEPE UNIVERSITY)0000-0001-5204-680X
Duru Karasoy(HACETTEPE UNIVERSITY)0000-0002-2258-4479
Pages
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Publication Date
2025-12-01
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AI Summary & Key Takeaways

AI Insight
⚡ TL;DR(Too Long; Didn't Read)

The results indicate that the linear time function (t) is more biased than the logarithmic time function (log(t)), which is a frequently used time function in modeling the hazard ratio.

📌 3 Key Takeaways

🎯
Objective & Hypothesis:Extended Cox regression model by using any form of time function is one of the alternative methods to the Cox regression model in non-proportional hazards case or time-dependent covariate problem.
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Key Findings & Data:This simulation study assesses the ability of the time functions for the extended Cox regression model in modeling non-proportional hazards according to sample sizes, censoring rate, and prevalence ratio of the binary covariate.
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Conclusion & Impact:The results indicate that the linear time function (t) is more biased than the logarithmic time function (log(t)), which is a frequently used time function in modeling the hazard ratio.
🔬Design:Modeling & Simulation
📍Scope:Comprehensive Sample
⚙️Variables:Extended Cox model · Time function · Non-proportional hazards

Abstract

Extended Cox regression model by using any form of time function is one of the alternative methods to the Cox regression model in non-proportional hazards case or time-dependent covariate problem. It is a key concern which time function should be used in which case for an extended Cox regression model. In this study, a comparison of the most commonly used time functions for the extended Cox regression model to obtain the effects of variables not satisfying the proportional hazard assumption is carried out. This simulation study assesses the ability of the time functions for the extended Cox regression model in modeling non-proportional hazards according to sample sizes, censoring rate, and prevalence ratio of the binary covariate. The results indicate that the linear time function (t) is more biased than the logarithmic time function (log(t)), which is a frequently used time function in modeling the hazard ratio. Also, it is shown that the use of time function 1/t has better results in most situations.

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Cite This Article

Işık, H., Tutkun, N. A., Karasoy, D. (2025). The Comparison of Time Functions in the Extended Cox Regression Model. Gazi University Journal of Science, Volume: 38 Issue: 4. https://doi.org/10.35378/gujs.1452842

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