We like to think of doctors as experts, whose recommendations are backed up by solid evidence. So why does it keep happening that a widely used medical intervention -- like estrogen replacement therapy, or heart stents -- turns out to be useless, or even harmful? This episode features Dr. Vinay Prasad, author of "Ending Medical Reversal: Improving Outcomes, Saving Lives," who talks with Julia about why medical research is so often fatally flawed, and what we can do about it.