When to randomize?

Many clinical trials address the question of the duration of therapy or whether initial therapy can be improved by the addition of a consolidation or maintenance regimen. For such clinical trials, the question of when to perform the randomization is often difficult. Conventional statistical wisdom prescribes that randomization should take place as late as possible before treatment is effected. This is not always possible or desirable, however. In this report, we describe the factors that are influenced by the timing of randomization, quantify how timing affects these factors, and attempt to provide a tool to help investigators and statisticians determine the appropriate time to randomize for individual studies and particular circumstances.