The function returns a dataframe with:
x1, x2, x3, x4, x5, x6= patient covariates.
t= treatment assignment (0 for control, 1 for active).
y.control= the outcome if the patient takes the control treatment.
y.active= the outcome if the patient takes the active treatment.
benefit= the treatment benefit, i.e. y.active-y.control.
y.observed= the observed outcome.