In landmark analyses I have seen, a common landmark time is chosen, say, 3 months after transplant, people are classified as having experienced rejection or not and then are followed until 60 months for various outcomes.
The scenario I’m looking at is a bit different. A study followed people from time of hospital admission to 1 year after the admission. People had various complications arise during their hospital stay, some died, but most lived to go home. At the time of hospital discharge, clinicians have to make decisions about plans for follow-up and additional tests to be done after someone is discharged so it is natural for them to want to know about the short to medium term prognosis of their patients who survived to discharge. I am considering setting the day of discharge from hospital as the landmark time (time 0) and setting as fixed covariates the medical events that occurred during the hospital stay (along with pre-hospital medical history, age, etc) and the dependent variable as some outcome (say mortality) that occurred between discharge and 1 year after hospital admission.
Note that the last possible day of follow-up is fixed at 1 year after hospital admission (not hospital discharge) so this creates a situation where maximum follow-up time varies with the duration of hospital stay. People who stayed in hospital longer will have shorter followups. In essence, they are censored earlier but the time to censorship is obviously going to be affected by the duration of hospital stay and duration of hospital stay likely carries prognostic information with respect to the outcome, so the censoring is informative. I suppose it is informative in a way where you are less likely to observe the outcome for people who stayed in hospital longer simply because you follow them for a shorter time. Of course, the outcome I think is more likely to occur sooner in these folks.
It seems to me that simply adjusting for the duration of hospital stay would attenuate the relationship between in-hospital complications (which will typically prolong length of stay) and the outcome. On the other hand, it is also possible that people who stayed in hospital longer had more time to have more complications observed and therefore classified as “in hospital” events, but I think the latter point is much less of an issue than the former.
Does anyone have insights into this? The lengths of stay are short (on the order of 1-3 weeks) compared to the duration of maximum followup and for this reason I suspect it will be a minor issue. I just have not seen such variable landmark times being used, where the landmark time is essentially patient-dependent.