Last year, Jonathan and I published a critique of unequal allocation ratios in late-phase trials. In these trials, patient-subjects are randomly allocated among the treatment arms in unequal proportions, such as 2:1 or 3:1, rather than the traditional equal (1:1) proportion. Strangely, despite introducing an additional burden (i.e., requiring larger sample sizes) the practice of unequal allocation is often defended as being “more ethical”. In that piece, published in Neurology, we showed that these purported ethical advantages of did not stand up to careful scrutiny.
In a new article at Clinical Trials, Jonathan and I extend this line of argument to trials that use outcome-adaptive allocation. In an outcome-adaptive trial, the allocation ratio is dynamically adjusted over the course of the study, becoming increasingly weighted toward the better-performing arm. In contrast to the fixed but unequal ratios described above, outcome-adaptive ratios can sometimes reduce the necessary sample size to answer the study question. However, this reduction in cost and patient burden is not guaranteed. In fact, it only occurs when the difference between the observed effect sizes is large. And since there is no way to know in advance what this difference is going to be, these potential gains in efficiency due to outcome-adaptive designs are something of a gamble.
Nevertheless, just as we saw with fixed unequal ratios, proponents of outcome-adaptive trials claim that this allocation scheme is “more ethical”. Setting aside the sample size issue, they argue that outcome-adaptive trials better accommodate clinical equipoise by collapsing the distinction between research and care. As it is sometimes put rhetorically: Would you rather be the last subject treated in a trial or the first subject treated in practice?
The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.