Views on allocation concealment methods in randomized clinical trials: a survey of clinical trialists

Abstract

<p>Allocation concealment is the process of implementing the randomization sequence in a manner that prevents foreknowledge of upcoming group assignments. It protects against preferential enrolment of study participants, which could disrupt the prognostic balance that randomization aims to create in the first place. Envelopes are one method perceived by clinical trial authorities to adequately conceal allocation, despite evidence suggesting otherwise. We do not believe that envelopes are adequate, and we wanted to know the extent to which our sentiment resonated within the clinical trials community. We administered an internet-based survey to a random sample (n=1,926) of corresponding authors of recently published randomized clinical trials (RCTs). We sent non-responders up to two e-mail reminders starting from two weeks after the original invitation. We received 490 complete surveys (25.4% response rate) after collecting data for seven weeks. Most participants (61%) preferred central randomization to conceal allocation, yet a majority (64%) also accepted that envelopes are adequate. After they were shown examples that suggested envelopes’ vulnerability, 11% of participants shifted their preference away from envelopes and 38% of participants became less accepting of envelopes. Compared to their initial ratings and after they were shown the examples, significantly more participants (69%) preferred central randomization (p</p>