  Various adaptive randomization procedures (adaptive designs) have been
proposed to clinical trials. This paper discusses several broad families of
procedures, such as the play-the-winner rule and Markov chain model, randomized
play-the-winner rule and urn models, drop-the-loser rule, doubly biased coin
adaptive design. Asymptotic theories are presented with several pivotal proofs.
The effect of delayed responses, the power and variability comparison of these
designs are also discussed.
