11.13 Proportional Hazards
The proportional hazards assumption states that (ISLR2 11.14):
h(t|xi)=h0(t)exp(p∑j=1xijβk)
Assumes separate time dependence (baseline hazard h0) from feature dependence.
Important to check proportional assumption!
Qualitative feature: plot the log hazard function for each level of the feature
Quantitative feature: stratify (
cut
) the feature and do the above.

Source ISLR Fig 11.4