This is only used in the simulation method for DesignGrouped to combine
the separately generated data sets from mono and combo arms and to fit the
combined logistic regression model.
Hence the ID and cohort information is not relevant and will be
arbitrarily assigned to avoid problems with the DataGrouped validation.
h_group_data(mono_data, combo_data)A DataGrouped object containing both mono_data and combo_data,
but with arbitrary ID and cohort slots.
(Data)
mono data.
(Data)
combo data.