Dear all,

I am doing a survival analysis on companies performance from year 1980 to 2010.
I want to see the difference of how many employees the company have between the observation year and the year of establishment , and how the difference is related to the performance of companies.
For some companies established before 1980, for example if I want to get the difference , should I compare the current year to the data from 1980 or the actual year of establish (e.g 1970)?

many thanks to your help!

best,
LB