John P. A. Ioannidis (born August 21, 1965 in New York City) is a Professor of Medicine and of Health Research and Policy at Stanford University School of Medicine and a Professor of Statistics at Stanford University School of Humanities and Sciences.
He is director of the Stanford Prevention Research Center, and co-director, along with Steven N. Goodman, of the Meta-Research Innovation Center at Stanford (METRICS). He was chairman at the Department of Hygiene and Epidemiology, University of Ioannina School of Medicine as well as adjunct professor at Tufts University School of Medicine. He is best known for his research and published papers on scientific studies, particularly the 2005 paper "Why Most Published Research Findings Are False". Ioannidis is one of the most-cited scientists across the scientific literature, especially in the fields of clinical medicine and social sciences, according to Thomson Reuters' Highly Cited Researchers 2015.
Born in New York City in 1965, Ioannidis was raised in Athens, Greece. He was Valedictorian of his class at Athens College, graduating in 1984, and won a number of awards, including the National Award of the Greek Mathematical Society. He also graduated in the top rank of his class at the University of Athens Medical School, then attended Harvard University for his medical residency in internal medicine. He did a fellowship at Tufts University for infectious disease and came to Stanford in 2010.
The Atlantic wrote a lengthy piece on Ioannidis in 2010.
The Economist wrote a shorter piece in 2014 about the foundation, by Ioannidis and Steven Goodman, of the Meta-Research Innovation Centre at Stanford.
He was profiled in the BMJ in 2015 and described as "the scourge of sloppy science".
Ioannidis's 2005 paper "Why Most Published Research Findings Are False" has been the most downloaded technical paper from the journal PLoS Medicine.
In another 2005 paper, Ioannidis analyzed "49 of the most highly regarded research findings in medicine over the previous 13 years". The paper compared the 45 studies that claimed to have uncovered effective interventions to subsequent studies with larger sample sizes: 7 (16%) of the studies were contradicted, 7 (16%) had effects that were smaller in the second study than in the first, 20 (44%) were replicated, and 11 (24%) remained largely unchallenged.
He has made many other influential empirical evaluations addressing the validation and replication performance of different types of studies in diverse scientific fields, including genetics, clinical trials, and neuroscience. His work has also aimed to identify solutions on how to optimize research practices and to increase the yield of validated and useful scientific findings.
He also coined the term Proteus phenomenon for the occurrence of extreme contradictory results in the early studies performed on the same research question. He has also made a number of contributions in the field of meta-analysis (the science of combining data from multiple studies on the same research question) and has been President of the Society for Research Synthesis Methodology.