Peter Dizikes: Writings on Science and Society

The Natural Experimenter
By Peter Dizikes. Technology Review, Jan/Feb 2013

Josh Angrist is an acclaimed experimentalist who does not work in a lab. The economist keeps a modest office in MIT’s Building E52, where the most prominent object is often a bicycle leaning against one wall. Compact and athletic, tan and graying, Angrist, 52, rides to work most mornings. In recent years he has spent weekends tearing around mountain-bike trails with riders half his age.

From these informal quarters, Angrist has built a kind of virtual laboratory of economics, where he generates precise answers to difficult social questions. As much as any scholar, he has helped popularize the idea that microeconomic research can, and should, imitate the conditions of lab experiments. Many other microeconomists base their work on models that make large assumptions about human behavior. But Angrist uses only empirical data that illuminate causal relationships in society.

Consider an issue Angrist has been pondering a lot lately: the effectiveness of high schools. To evaluate schools, you might compare test scores, graduation rates, or college acceptance data. Yet it could just be that the top-rated school districts attract a greater proportion of families with well-prepared students.

Scholars can’t answer questions like this by randomly assigning students to schools themselves and studying the results. So to gain traction on such slippery problems, Angrist relies on natural experiments—cases in which two otherwise similar groups of people have been distinguished by one particular circumstance. If, say, a school district line is redrawn, instantly transferring one group of students to a new school, it might create what economists call a “clean identification” of cause and effect that isolates the schools’ own impact.

Over two decades, Angrist’s natural experiments have made him a prominent figure within economics. As of August, he was one of the 100 most-cited economists in the world, according to the Federal Reserve Bank of St. Louis, which keeps data on more than 33,000 authors. Among his best-known papers are studies on the relationship between length of schooling and income; the effect military service has on earnings; and the link between class size and student achievement.

Angrist did not invent his quasi-¬≠experimental methods; they were largely popularized from the 1980s onward by a group of prominent economists including Alan Krueger (currently chair of the White House’s Council of Economic Advisers), with whom Angrist has co-authored multiple papers; Lawrence Katz of Harvard University; David Card, now of the University of California, Berkeley, who was one of Angrist’s graduate-school advisors; and Angrist’s principal mentor, Orley Ashenfelter of Princeton University. But no one has been a more staunch advocate of lab-like economics.

“He’s had tremendous influence,” says Whitney Newey, PhD ’83, chair of MIT’s Department of Economics, who was one of Angrist’s graduate-school advisors.

Angrist’s citation ranking within economics probably understates that influence. Biostatisticians, who study cause and effect in medicine and biological research, regularly cite his methods, and political scientists and sociologists have adopted natural experiments as a basic research tool as well. Esther Duflo, PhD ’99, a prominent antipoverty researcher at MIT whom Angrist advised when she was a graduate student, says his relentless concentration on the problem of selection bias—for instance, the possibility that the better-rated high school is populated with better students—spurred her to go beyond his techniques and conduct actual field experiments. “Once you ask the question right, you can ask what the ideal experiment to answer it is,” she explains. “Josh [is] a champion of natural experiments, but that is also the work that [has] led many of us to think that true randomized experiments could be a very promising way to go.”

Yet if Angrist’s CV bears the markings of an academic star—PhD from Princeton, first job at Harvard, and a named chair at MIT, where he is the Ford Professor of Economics—his life could have been very different. Angrist left high school after the 11th grade, having completed the bare minimum of coursework needed to graduate. He took time off before deciding to go to college, dropped out of grad school, and then served in the Israeli army before pursuing a PhD in economics.

“I got a lot of lucky breaks in my life,” he says.

Angrist doesn’t think his research agenda, with its emphasis on the difference that education makes, has been driven by his own past. In economics, he says, it’s “a mistake to learn from your own experience” rather than being guided by data and a desire to study important topics. Still, it helps to know a little about Angrist in order to better understand his work, in part because he likes to probe the idea that contingent social circumstances can put otherwise similar people on different paths. After all, he himself could have gone in a few other directions—something that “colors my view of the world,” he acknowledges.

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My work has appeared in The New York Times, The Boston Globe, The Washington Post, Slate, Salon, Technology Review, and numerous other publications. You can learn more about me here.


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