Table 1: Options available at interim analysis (IA) in a 2-subgroup direct assignment design with 1 IA (DAD-1) versus a 2-subgroup balanced randomized design with 1 IA (BRD-1). The decisions are independently made in each subgroup at the time of IA. Some cells in the BRD-1 table are intentionally left blank, to highlight the missing option of direct assignment in this design. The options in bold are those that are available only in the design with direct assignment option.

Options at interim analysis (IA)
2-subgroup direct assignment design with 1 IA (DAD-1)2-subgroup balanced randomized design with 1 IA (BRD-1)
M−M+M−M+

Stop, futilityStop, futilityStop, futilityStop, futility
Continue, randomizeContinue, randomize
Continue, direct
Stop, efficacyStop, efficacy

Continue, randomizeStop, futilityContinue, randomizeStop, futility
Continue, randomizeContinue, randomize
Continue, direct
Stop, efficacyStop, efficacy

Continue, directStop, futility
Continue, randomize
Continue, direct
Stop, efficacy

Stop, efficacyStop, futilityStop, efficacyStop, futility
Continue, randomizeContinue, randomize
Continue, direct
Stop, efficacyStop, efficacy