Box 55 Desirable features of sample size software for timetoevent data

♦ Formulae are based on published methods

♦ Will derive both number of events and number of patients required

♦ Allows incorporation of estimates of accrual rates and follow-up periods

♦ Allows for unequal randomization

♦ Allows for differential drop-out and/or withdrawal rates across arms is important to know both, and the provision of both is a good feature to look for in purchasing books or software. Other important features to look out for in software to calculate sample sizes for time-to-event studies are shown in Box 5.5.

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