Factor covariates can give trouble in multi-session models if the levels differ among sessions. A warning is provided by verify.capthist. This function forces factor covariates to use the same levels.
shareFactorLevels(object, columns = NULL)An object of the same class as input.
Factor-valued covariates are coerced to use the same set of levels for each session of a multi-session capthist object or each component of a list of traps or masks. The combined level set is the union of all levels in separate sessions. The order of levels follows the default in factor (alphabetical).