Marcia Angell was an editor of the most prestigious medical journal in the world for two decades. She currently gives monthly lectures on ethics to faculty at Harvard Medical School. And she served on a panel that gave advice on medical issues to the White House. But Dr. Angell’s credentials were challenged, Wednesday, in the Supreme Court of British Columbia when a lawyer for the federal Department of Justice tried to prevent her affidavit from being entered in a case concerning physician-assisted suicide.