Represents Wei's Urn Design.
udPar(N, ini, add, groups = LETTERS[1:2])integer for the total sample size of the trial.
integer representing the initial urn composition.
integer representing the number of balls that are added to the urn in each step.
character vector of labels for the different treatments.
S4 object of the class udPar.
An urn is filled with a number of ini balls of both of the treatments.
Afterwards, a ball is drawn randomly from the urn. Finally, add balls
are added to the urn from the opposite treatment. This procedure is repeated until
N patients are assigend.
L.J. Wei (1977) A Class of Designs for Sequential Clinical Trials. Journal of the American Statistical Association, 72, 382-6.
Other randomization procedures: abcdPar,
bbcdPar, bsdPar,
chenPar, crPar,
createParam, ebcPar,
gbcdPar, hadaPar,
mpPar, pbrPar,
rarPar, rpbrPar,
rtbdPar, tbdPar