Are outcome-adaptive allocation trials ethical?

Clin Trials. 2015 Apr;12(2):102-6. doi: 10.1177/1740774514563583. Epub 2015 Feb 3.


Randomization is firmly established as a cornerstone of clinical trial methodology. Yet, the ethics of randomization continues to generate controversy. The default, and most efficient, allocation scheme randomizes patients equally (1:1) across all arms of study. However, many randomized trials are using outcome-adaptive allocation schemes, which dynamically adjust the allocation ratio in favor of the better performing treatment arm. Advocates of outcome-adaptive allocation contend that it better accommodates clinical equipoise and promotes informed consent, since such trials limit patient-subject exposure to sub-optimal care. In this essay, we argue that this purported ethical advantage of outcome-adaptive allocation does not stand up to careful scrutiny in the setting of two-armed studies and/or early-phase research.

Keywords: Adaptive randomization; equipoise; ethics; therapeutic misconception.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Humans
  • Randomized Controlled Trials as Topic / ethics*
  • Research Design*