In R, to check if the proportional hazards assumption is met, we can run the cox.zph command to plot the scaled Schoenfeld residuals vs time. But what does zph actually stand for? I'd imagine that the ph stands for proportional hazards, but I am unsure what z stands for.
I want to know what it stands for because
- "checking scaled schoenfeld residuals vs time" is a mouth full to say
- "running zph" doesn't convey details to somebody unfamiliar with the model