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.

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

“Card’s studies of core questions for society and Angrist and Imbens’ methodological contributions have shown that natural experiments are a rich source of knowlege,” said Peter Fredriksson, chair of the Economic Sciences Committee. “Their research has substantially improved our ability to answer key causal questions, which has been of great benefit for society.”

Unlike the other Nobel prizes, the economics award wasn’t established in the will of Alfred Nobel but by the Swedish central bank in his memory in 1968, with the first winner selected a year later. It is the last prize announced each year.

Read:Tanzanian Abdulrazak Gurnah awarded Nobel literature prize

Last week, the 2021 Nobel Peace Prize was awarded to journalists Maria Ressa of the Philippines and Dmitry Muratov of Russia for their fight for freedom of expression in countries where reporters have faced persistent attacks, harassment and even murder.

Ressa was the only woman honored this year in any category.

The Nobel Prize for literature was awarded to U.K.-based Tanzanian writer Abdulrazak Gurnah, who was recognized for his “uncompromising and compassionate penetration of the effects of colonialism and the fate of the refugee.”

The prize for physiology or medicine went to Americans David Julius and Ardem Patapoutian for their discoveries into how the human body perceives temperature and touch.

Read: Nobel in chemistry honors 'greener' way to build molecules

Three scientists won the physics prize for work that found order in seeming disorder, helping to explain and predict complex forces of nature, including expanding our understanding of climate change.

Benjamin List and David W.C. MacMillan won the chemistry prize for finding an easier and environmentally cleaner way to build molecules that can be used to make compounds, including medicines and pesticides.