Ngày đăng : 14/06/2022
The continuous predictor X is discretized into a categorical covariate X ? with low range (X < X1k), median range (X1k < X < Xdosk), and high range (X > X2k) according to each pair of candidate cut-points.
Then the categorical covariate X ? (source top 's the median diversity) is equipped inside a good Cox model therefore the concomitant Akaike Advice Standards (AIC) worthy of is determined. The two from slash-issues that decrease AIC beliefs is understood to be max clipped-circumstances. More over, choosing slashed-factors by Bayesian pointers standards (BIC) gets the exact same efficiency due to the fact AIC (Additional file step one: Dining tables S1, S2 and S3).
The optimal equal-HR method was implemented in the language R (version 3.3.3). The freely available R package ‘survival' was used to fit Cox models with P-splines. The R package ‘pec' was employed for computing the Integrated Brier Score (IBS). The R package ‘maxstat' was used to implement the minimum p-value method with log-rank statistics. And an R package named ‘CutpointsOEHR' was developed for the optimal equal-HR method. This package could be installed in R by coding devtools::install_github(“yimi-chen/CutpointsOEHR”). All tests were two-sided and considered statistically significant at P < 0.05.
An effective Monte Carlo simulation analysis was used to evaluate the latest efficiency of your optimum equal-Hour method or any other discretization methods for instance the average split up (Median), the top of and lower quartiles beliefs (Q1Q3), as well as the lowest record-score take to p-value means (minP). To investigate the fresh overall performance of them tips, the fresh new predictive overall performance out-of Cox models suitable with assorted discretized details is analyzed.
U(0, 1), ? was the size factor out-of Weibull delivery, v is actually the shape parameter away from Weibull shipping, x was an ongoing covariate from a fundamental typical shipment, and you can s(x) are the brand new given function of interest. So you can replicate U-designed matchmaking ranging from x and you will record(?), the type of s(x) is set to become
where parameters k1, k2 and a were used to control the symmetric and asymmetric U-shaped relationships. When -k1 was equal to k2, the relationship was almost symmetric. For each subject, censoring time C was simulated by the uniform distribution with [0, r]. The final observed survival time was T = min(T0, C), and d was a censoring indicator of whether the event happened or not in the observed time T (d = 1 if T0 ? C, else d = 0). The parameter r was used to control the censoring proportion Pc.
One hundred independent datasets were simulated with n = 500 subjects per dataset for various combinations of parameters k1, k2, a, v and Pc. Moreover, the simulation results of different sample sizes were shown in the supplementary file, Additional file 1: Figures S1 and S2. The values of (k1, k2, a) were set to be (? 2, 2, 0), (? 8/3, 8/5, ? 1/2), (? 8/5, 8/3, 1/2), (? 4, 4/3, ? 1), and (? 4/3, 4, 1), which were intuitively presented in Fig. 2. Large absolute values of a meant that the U-shaped relationship was more asymmetric than that with small absolute values of a. Peak asymmetry factor of the above (k1, k2, a) values were 1, 5/3, 3/5, 3, 1/3, respectively. The survival times were Weibull distributed with the decreasing (v = 1/2), constant (v = 1) and increasing (v = 5) hazard rates cheekylovers chat. The scale parameter of Weibull distribution was set to be 1. The censoring proportion Pc was set to be 0, 20 and 50%. For each scenario, the median method, the Q1Q3 method, the minP method and the optimal equal-HR method were performed to find the optimal cut-points.
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