So it's preferable to do the riskier studies on people with less risky options?

It's more a case of a lot of studies are intentionally being designed to focus on early diagnosis, early intervention type stuff. Of the set of 'Clinical Research Studies' a small portion are on high risk, ethically difficult populations. As it is, my research is difficult enough because we are asking people to participate in research in the same setting where they are receiving some of the highest quality care possible for the disease, which borders on ethically sticky. Lots of cardiologists have patients with this diagnosis, but not a lot of cardiologists have outcomes like my team, so we have to be very careful about how we approach the consenting process. We have an incredibly low threshold for disqualifying someone we believe is feeling forced to participate including kids not wanting to spend a whole day in the hospital getting poked, prodded and stared at. And that's for relatively non-invasive, low-risk procedures and interventions.