Abstract: AIM: Previous studies have suggested that big stick design (BSD) method can only be used in clinical trials of two treatments with equal proportion, which has good statistical performance and has become the recommended choice of randomized methods. This study expands BSD meth-od, so that it can be applied to three groups, and provides more randomized methods for clinical trials. METHODS: On the basis of BSD method used in two treatments with equal proportion, the derivation conditional allocation probability of BSD meth-od used in three treatments with equal proportion was carried out. BSD method was compared with simple randomization (SR) method, permuted block design (PBD) method and block urn design (BUD) method by Monte-Carlo simulation in balance and randomness. RESULTS: In terms of balance, PBD method was the best, followed by BUD method, BSD method, and SR method was the worst. In terms of randomness, SR method was the best, followed by BSD method, BUD method and PBD method. The comprehensive performance showed that BSD method was better than BUD method, PBD method and SR method. CONCLUSION: The expanded BSD method used in three treatments with equal proportion has good comprehensive performance, and it can be the recommended randomization method for clinical trials of three treatments with equal proportion.

Key words: randomization, simple randomization, permuted block design, big stick design, block urn design