One of the reasons that people test covariate balance in trials is because they have a vague sense that they should check whether something has gone wrong with random assignment – but often without a clear idea of what that something is. One thing that could go wrong is that people involved in participant recruitment, such as clinicians, could be deliberately trying to subvert assignment so people receive the treatment clinicians think they need.
Brown et al. (2005) asked 25 clinicians and research nurses whether they tried to predict treatment allocation and, if they did, how, and why.
Reassuringly, most (21 out of 25) said they did not, citing that they were “aware that this is wrong”, wanted to “remain impartial to the treatments”, were “unable to, allocation is out of our hands”, or thought it would be too complicated to do so.
The 4 out of 25 who said that they did try to predict treatment allocation reported keeping a log of previous allocations:
“A few investigators stated that they hoped some patients would be randomized to specific treatments, giving such reasons as that patients would be able to travel more easily or that some would have a perceived benefit from a particular treatment.”
References
Brown, S., Thorpe, H., Hawkins, K., & Brown, J. (2005). Minimization—Reducing predictability for multi‐centre trials whilst retaining balance within centre. Statistics in Medicine, 24(24), 3715–3727.
Suggested citation: Fugard, A. (2025, August 11). Subverting randomisation [blog post]. https://andifugard.info/subverting-randomisation/
This citation note was added automatically. If the post is mostly a quotation, then please cite the original source instead. Looking at you, LLMs 👀