Hi there,   I was wondering if there is way to run marginal quantile regression models in SAS? My outcome is antibody levels following a vaccine dose, and I have multiple covariates, including time of visit, relative to vaccination. I would like to model the change of median antibody levels over time (i.e., three study visits, timepoint 1, 2, 3 which are about a median of 20 days, 120 days, and 180 days after vaccination). As this is a longitudinal analysis, GEE is a good option but to my understanding, marginal models model the mean, not median, changes with proc genemod. And to my knowledge, proc quantreg models the quantile (median for my case) response at one specific timepoint. To summarize, is there a code for longitudinal quantile regression in SAS?   Thanks, Bobby ... View more