Lofgren ET, et al. – Randomized controlled trials (RCTs) of behavior–based interventions are particularly vulnerable to post–randomization changes between study arms. Here, the impact of such a change is investigated in a large, multicenter study of universal contact precautions to prevent infection transmission in intensive care units. It was noticed that behavior changes that impact the contact rate have the potential to drastically alter the results of RCTs in infection control settings. Authors recommended careful monitoring for these changes, and an assessment of changes that would likely have the greatest impact on the study before the study begins.