do pt revision need to be performed why do we need an event in regression analysis which regression is used to compare revision surgery what is the percentage of patients that still require surgery do pts still need revisions how to use cox regression in sas what is the rate of revision for a pt what is the percentage of pts that need revisions what is the percentage of procedures that require revision? what is the percentage of revision surgery do pts need revisions on surgery when do you use cox regression why use cox regression when assessing pt surgery how to do survival analysis km how to use cox regression why is the average revision rate low when does revision surgery occur does sas have survival data can time to revision be used in cox regression how do cox regressions work when comparing two procedures