I would like to ask whether it is possible to have a retrospective survival analysis.
We have a population of patients who had an examination twice (one now and one in past with varying time intervals). We measure at the time of the latter examination a specific gene, which of course is a constant factor through time and we are interested in a finding of the examination.
Is it correct to run a survival analysis for that finding between the gene groups? The concept is that the population basically existed in the first examination although formed by our measurement in the second.