The survival analysis plays a vital role in analyzing time-toevent data [ , ]. Among several proposed prediction models, the semiparametric Cox regression model has gained widespread use in the field of medical research because no distribution assumption is required of the probability of survival times and it usually fits the data well [ - ]. The “semiparametric” term is used in the Cox model since it does not assume any distribution of survival times (nonparametric), but it estimates the regression coefficient based on the model (parametric). The risk of an independent variable is constantly proportion, but the relative risk does not change over time ( ).
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