BASIC RESEARCH + SOCIAL INNOVATION
The “metrics” system
How to conduct cause-and-effect studies on complex social questions
“People are constantly looking at the world around them and trying to learn from it, and that’s natural,” MIT economist Joshua Angrist says. “But it turns out to be very difficult to sort out cause and effect, because the world is complicated, with many things happening at once.”
If you would like to produce good quantitative social-science research, try remembering these two words: “ceteris paribus.”
That’s Latin for “other things being equal.” And it’s a key principle when designing studies: Find two groups of people who, other things being equal, are distinguished by one key feature.
Consider health care. If you can find two otherwise equal groups of people who differ only in terms of health care coverage — one group has it, one doesn’t — then you may be able identify a causal relationship at work: What difference does it make when people get health insurance?
Without such a research strategy, scholars can be left staring at a tangle of potential causes and effects. Suppose you have one group of people with health insurance, and one without — but the insured people are wealthier. Are they better off financially because they have insurance, or do they have insurance because they’re better off financially? It may be hard to know. You need groups of equal wealth to solve the causation conundrum.
“People are constantly looking at the world around them and trying to learn from it, and that’s natural,” MIT economist Joshua Angrist says. “But it turns out to be very difficult to sort out cause and effect, because the world is complicated, with many things happening at once.”
Angrist, the Ford Professor of Economics, has long been one of the leading advocates of research that uses “ceteris paribus” principles. Now, along with Jorn-Steffen Pischke of the London School of Economics, Angrist has written a book on the subject for a general audience, Mastering ‘Metrics: The Path from Cause to Effect, published this month by Princeton University Press.
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