For randomized group sequential survival trial designs with unbalanced treatment allocation, the widely used Schoenfeld formula is inaccurate, and the commonly used information time as the ratio of number of events at interim look to the number of events at the end of trial can be biased. In this article, a sample size formula for the two-sample log-rank test under the proportional hazards model is proposed that provides more accurate sample size calculation for unbalanced survival trial designs. Furthermore, a new information time is introduced for the sequential survival trials such that the new information time is more accurate than the traditional information time when the allocation of enrollments is unbalanced in groups. Finally, we demonstrate the monitoring process using the sequential conditional probability ratio test and compare it with two other well-known group sequential procedures. An example is given to illustrate unbalanced survival trial design using available software. Supplementary materials for this article are available online.

对于治疗分配不平衡的随机分组连续生存试验设计，广泛使用的Schoenfeld公式是不准确的，并且常用的信息时间（即临时事件数与试验结束时事件数之比）可能存在偏差。在本文中，提出了比例风险模型下两样本对数秩检验的样本大小公式，该公式为不平衡的生存试验设计提供了更准确的样本大小计算。此外，为顺序生存试验引入了新的信息时间，这样当分组分配不均衡时，新的信息时间比传统的信息时间更准确。最后，我们演示了使用顺序条件概率比率检验的监视过程，并将其与其他两个众所周知的小组顺序过程进行了比较。举例说明了使用现有软件进行的不平衡生存试验设计。可在线获得本文的补充材料。