Rate question

[curiosgeorge]

Hi all! I have a dataset of a retrospective matched cohort study of cases and controls together. I am interested to know if a lookback injury rate before an index date into study, can be used as a predictor variable for a time to first injury Cox model post-index date. I was thinking of doing a number of events divided by person years sort of idea. Can someone offer their insights on this? Also if you can show me the code for doing this, I would be very grateful!