How often do today’s medical “breakthroughs” become tomorrow’s discredited science? John P. A. Ioannidis, an epidemiologist at Tufts University School of Medicine in Boston and the University of Ioannina School of Medicine in Greece, studied the question. He examined the most-cited clinical studies published in the top three medical journals between 1990 and 2000 to see how well researchers’ initial claims held up against subsequent research. His findings, published in JAMA, show that the key claims of nearly one-third (14 out of 49) of the original research studies he examined were either false or exaggerated. Small study size, design flaws, publication bias (failure to publish negative results or duplication of positive results), drug-industry influence, and the play of chance were among the problems Ioannidis found that caused false or exaggerated claims.