This function check these differents topic: Outcome must be binary and a
factor. If numeric with two distincts values, outcome becomes a factor where
the favorable reponse is the second level. Also, outcome is moved on the
first column of dataset
.
Treatment must have two distinct numeric values, 0 : no treatment, 1 :
treatment. Treatment is moved to the second column.
Qualitatives variables must be factor. If it has more than two levels, if
running VirtualTwins with interaction, it creates dummy variables.