Wei's urn design was proposed in 1987 for subject randomization in trials comparing m ≥ 2 treatments with equal allocation. In this manuscript, two modified versions of Wei's urn design are presented to accommodate unequal allocations. First one uses a provisional allocation of [Formula: see text] to achieve the target allocation r1 : r2, and the second one uses equal allocation for r1 + r2 arms to achieve an unequal allocation r1 : r2 based on the concept Kaiser presented in his recent paper. The properties of these two designs are evaluated based on treatment imbalance and allocation predictability under different sample sizes and unequal allocation ratios. Simulations are performed to compare the two designs to other designs used for unequal allocations, include the complete randomization, permuted block randomization, block urn design, maximal procedure, and the mass weighted urn design.
Keywords: randomization; unequal allocation; urn design.