Why most published research is false — John Ioannidis and the replication crisis

John Ioannidis was a Greek-American physician-scientist trained at Harvard and Tufts, with a PhD in biopathology. On August 30, 2005, he published a paper in PLOS Medicine titled 'Why Most Published Research Findings Are False.' It became the most-accessed article in PLOS history, with over 3 million views. Ioannidis argued that a research finding is less likely to be true when studies are small, effect sizes are small, tested relationships are numerous, and financial interests are present.

The paper systematically showed how the scientific method was being undermined by its own incentives. Journals wanted novel positive findings, so researchers produced them — often by p-hacking, selective reporting, and running small underpowered studies. Ioannidis later catalogued 235 biases in biomedical research and found that at least 1 in 6 widely cited health studies were later contradicted. In economics, nearly 80% of reported effects were exaggerated, typically by a factor of two, with one-third inflated by four or more.

The paper made Ioannidis a central figure in the replication crisis that swept through psychology, medicine, economics, and neuroscience. He co-authored the Manifesto for Reproducible Science and co-directed the Meta-Research Innovation Center at Stanford (METRICS). The crisis exposed a system that had been producing false findings for decades — not because of fraud, but because the incentives rewarded the wrong kind of science.