reults$derived in multistate robust design formulations

[ricardo]

I have been trying to fit multistate robust design models via RMark, but whatever the model type I specified (ORDPdMS, CRDMSOHug, CRDMSOHet, CRDMSOFHet), and the combination of individual or design covariates tested on each parameter considered in each case (including models without covariates), the results$derived for population size estimation invariably returns NULL.
Ricardo