If you have primary data, there exist several ways to calculate a risk difference (RD) or number needed to treat (NNT) from time-to-event data (see e.g. following pmid: 29955580, 31626655). However, I am performing a meta-analysis yielding a summary-HR, based on Cox regression models which were adjusted for different covariables. I have no primary data.
What I do have, on the other hand, is the number of participants at risk (crude or in person years, depending on study design) and the number of events.
My question is: Is is possible to calculate a risk difference based on my summary HR in this case?