I'm trying to use some form of survival analysis (e.g. accelerated failure time or proportional hazards) to study seed germination time. My data is interval censored (also called "grouped-time") and has a random effect (also called "frailty"). How can I do this, ideally in SAS?
My seeds were on petri dishes that were censused on day 1, 3, 5, 8, and 14. These are interval censored, with a seed that germinated on d8 really germinated between day 6 and day 8.
PROC LIFEREG can handle interval censoring but as far as I know, it doesn't handle random effects. Seeds on the same petri dish are not independent, so I need to be able to include the dish as a random effect. I would like to make inferences about the mean or median time to germination for a seed grown under several treatment conditions (e.g. genotype, maternal temperature, seed temperature, & interactions)
Is there an approach that allows interval censoring as well as random effects? If so, how should I modify the SAS code below to include random effects? Do I need to switch procedures to something like
PROC NLMIXED? If this is something that cannot be done in SAS, what software is the best/easiest to do this?
PROC LIFEREG DATA=survGeno2 plots=probplot; TITLE "Interval censored AFT"; CLASS geno; MODEL (start,fin)=geno; RUN;