Three U.S-based economists won the 2021 Nobel prize for economics on Monday for work on drawing conclusions from unintended experiments, or so-called “natural experiments.”

David Card of the University of California at Berkeley was awarded one half of the prize, while the other half was shared by Joshua Angrist from the Massachusetts Institute of Technology and Guido Imbens from Stanford University.

The Royal Swedish Academy of Sciences said the three have “completely reshaped empirical work in the economic sciences.”