For Emily F. Oster ’02 economics is about more than supply and demand. The 24-year-old has conducted research on topics from witch trials to AIDS—and she’s only a second-year Ph.D. student at the Graduate School of Arts and Sciences.

“For me, this has been the happiest and most productive part of my life,” said Oster.

Oster added another impressive item to her résumé last Sunday when the New York Times featured her theory linking the rise of witch trials to bad weather in its “Year in Ideas” article—an annual collection of “the most noteworthy ideas of the previous 12 months.”

Oster’s theory, which was originally published in last winter’s Journal of Economic Perspectives, connects the period of cold weather in Europe known as the “little ice age” to an increase in witch trials from 1520 to 1770. Oster hypothesizes that after climate conditions devastated crops, Europeans looked for someone to hold accountable—eventually resulted in the burning of tens of thousands of witches.

“When economic times are bad, people look for someone to blame,” Oster explained. “The fact that there were more trials during worse weather means that witches were a scapegoat.”

Jones Professor of Economics Andrei Shleifer, also her Ph.D. adviser, said that what separates Oster from other scholars is her ability to tackle world issues with ease.

“She goes for extremely big problems and she makes progress,” he said. “She is quite remarkable for someone in their second year as a graduate student,” he said.

Oster’s theory was the result of months of research on temperature patterns and witch trial chronology. Oster said she first grew interested in witches and weather from a course she took as an undergraduate at Harvard.

But it was not until later in her college career that she made a link between the trials and weather patterns.

“I was totally fascinated with all of that stuff,” she said. “The fact that I connected witchcraft to weather was only because I happened to be, at that time, reading for pleasure about the little ice age.”

In addition to her witchcraft theory, Oster has written extensively on the topic of AIDS.

She is comparing statistics in Africa to U.S. numbers in hopes of discovering why infection rates vary so much across borders.

Although the paper is still in the works, Gates Professor of Developing Societies Michael Kremer, one of Oster’s Ph.D. advisers, said her work reflects the growing trend toward development economics.

“She is part of a broader resurgence of interest in the economics of developing countries among graduate students at Harvard,” Kremer wrote in an e-mail.

The ability to explore issues as diverse as witches and war is what Oster said she likes best about economics.

“What I think is so great about economics is that I get interested in stuff based on things I read and things I see,” she said. “The scope of the field is very broad, but you’ve got to think outside the box.”

In 2002, University President Lawrence H. Summers, unbeknownst to Oster, mentioned her witch-weather theory in his Commencement speech.

“Right before he mentioned my research he talked about a physicist that stopped light or something,” she said. “I thought to myself ‘This is totally out of proportion.’”

Oster said she is currently researching the correlation between the number of men in a country and the possibility that the country will go to war. She is also exploring sex ratios in Asia and how it relates to the Hepatitis B virus. Beyond those endeavors, she said she is always on the lookout for future topics. “I think I take it as it comes,” she said.