concurrent controls in platform trials</h2>
<p>Platform trials are multi-arm multi-stage clinical trials that aim at
evaluating the efficacy of several treatment arms within a single trial.
Experimental treatments are permitted to enter and exit the trial at
different times, as new treatments become available, and the total
number of newly added treatments is not pre-specified. Moreover,
treatment arms may be compared against a shared control group.</p>
<p>For treatments that enter the trial later, t