Videos (English)

Paris IAS Ideas - What is bias? And why are we biased?

IEA de PARIS / 14.11.2025

Description: Lecture as part of the "Paris IAS Ideas" series. These short presentations mark the beginning of one-month writing residencies during which visiting scholars write an article presenting the "definitive" version of an idea or concept they have been working on for years. Online lecture by Gerd Gegerenzer, former Director of the Max Planck Institute for Human Development, Director of the Harding Center for Risk Literacy at the University of Potsdam, and Vice-President of the European Research Council (ERC). He is a fellow in writing residency in November 2025 at the Paris IAS.

What is bias? And why are we biased?

Presentation: This project explores the concept of ‘bias’ and the multiple ways in which it is interpreted. The same behaviour can seem both rational and irrational: following base rates is consistent with Bayes, but can be perceived as prejudice. A similar tension arises between disciplines: in behavioural economics, rationality is synonymous with absence of bias, while in machine learning, a certain amount of bias is essential to produce reliable predictions and avoid overfitting. The online conference will propose that this contradiction can be resolved by Savage and Simon's distinction between ‘small worlds’ and ‘big worlds’. In a small, perfectly known world, bias is harmful. But in the uncertainty of large worlds, it becomes a rational and functional tool: bias is no longer a flaw, it is a strategy.