why does cox.zph use a function what is the ratio of y value for cox.zph? what is the hr of cox cox zph function r how to plot proportional hazards in r what is the function that plots the r curve what is cox zph in the r what does cox hazard plot stand for what is the function of cox.zph for r what is cox vs coxph what is the function of cox zph what is the hr in a cox proportional hazard model what is r.p plot what is the cox.xph what is the plotted value of the cox what is the function of r cox how to do plotted cox hazard in r what is the plot value of cox.zph? what is the plotting formula for cox zph what is the function for cox.zph in r