Setup outcome for longitudinal marker (internal function) input:
setup_Y_model(formula, dataset, family, k)
YL.name name of the outcome
YL values of the outcome
with lme4 format (fixed effects and random effects in the same object)
that contains the outcome
of the outcome (given to check if the distribution matches but the check is not done yet)
identifies the longitudinal marker among 1:K markers output: