Clinical trials are complicated enough when everything goes pretty much as expected. When it doesn't, the dilemma of continuing or stopping can be excruciatingly difficult. Some of the greatest dramas in clinical research are going on behind the scenes around this. Even who gets to call the shot can be bitterly disputed. A trial starts with a plan for how many people have to be recruited to get an answer to the study's questions. This is calculated based on what's known about the chances of benefits and harms, and how to measure them. Often a lot is known about all of this. Take a trial of antibiotics, for example. How many people will end up with gastrointestinal upsets is fairly predictable. But often the picture is so sketchy it's not much more than a stab in the dark. Not being sure of the answers to the study's questions is an ethical prerequisite for doing clinical trials. That's called equipoise. The term was coined by lawyer Charles Fried in his 1974 b...