obs observed data from .rep file pred predicted data from .rep file (if used) rec_age recruitement age plus_age plus age group comp age or length - default is length lenbins set to base unless using alt in which case the file should be in the user_input folder and the name needs to be provided e.g., lengthbins.csv - the column must be named len_bin
purrit(obs, pred = NULL, rec_age, plus_age, comp = "length", lenbins = NULL)