# Follow-up time with too many zeros?

I have a dataset of 1500 patients for a time-to-event study. Almost half the population died at the moment of inclusion into the study which means that they have had a follow-up time of zero. Now I want to report the follow-up time which is around 5 days while the surviving patients were followed up for several years.

Is that a problem that needs solving? I have a feeling that this is not representative of my study population. I have looked at the reverse-kaplan-meier method but I dont know if that is applicable to my current situation.

• I'm confused by the issue. A population with half the members dying instantly and the other half surviving for several years should have a mean follow-up time measured in years, not days. Statistics properly computed from a population should of course be representative of that population, but I don't understand what that 5 day number is supposed to represent. Jan 14 at 19:52
• Due to the index event being cardiac arrest (which is associated with a high risk of death) the proportion of people who survive the event is very low. The rest may live for a short while and pass away then. This is how the 5 days came to be. The rest of patients have survived years without issue. I hope this clarifies any confusions. Jan 14 at 20:08
• Why not subdivide your population, much as is done for life expectancy estimates where deaths during or immediately after birth are separated? In other words, report separately on those who died within a defined short period after inclusion.
– whuber
Jan 14 at 20:35