Hypothetical intermediate results at the end of an intermediate trial stage. HR = Hazard ratio; CI = Confidence interval. In this example, the research arms are drug A, drug B and the combination of drugs A and B; the common control arm is neither drug. The guideline for continuation of recruitment into the next stage is 0·92 compared with the control arm. The research arms containing drug B and drug A+B have met the criteria in this instance; the arm containing drug A has not met the criteria but is showing some evidence of an advantage in terms of the intermediate outcome measure. In this instance and in the absence of safety concerns, the IDMC may decide that recruitment should be continued to all 3 arms.