The colleague, of course, was right, Mullainathan concedes; economics is the study of how people manage physical scarcity. But even though actual scarcity is ubiquitous—there are always limits to time, food, and money—the feeling of scarcity is not, he explains. This overpowering mindset was what he and Shafir were interested in studying, and it had effects, they argued, that could be quantified and explored empirically.
In 2010, the authors and their colleagues set out to do that—setting up scientific trials in what Mullainathan jokingly calls “the best lab in the world”: a shopping mall in New Jersey. The group hoped to show in an experiment that poverty imposed a kind of “bandwidth tax” that impaired people’s ability to perform. “To put it crudely,” he explains, “poverty—no matter who you are—can make you dumber.”
To prove it, they planned to administer Raven’s Progressive Matrices tests (essentially IQ tests that measure skills without requiring experience or expertise) to their subjects. Just before taking the test, subjects were asked to consider a hypothetical scenario:
Imagine you’ve got car trouble and repairs cost $300. Your auto insurance will cover half the cost. You need to decide whether to go ahead and get the car fixed,or take a chance and hope that it lasts for a while longer. How would you make this decision? Financially, would it be easy or hard?
Using self-reported household income, the researchers split the subjects into groups of “rich” and “poor.” When they tallied their scores on the Raven’s Matrices, there was no statistically significant difference in the groups’ performance.
But in a second version of the test, researchers raised the price tag for the repairs to $3,000. Although rich people’s test scores showed no significant difference, the poor people’s scores dropped the equivalent of about 14 IQ points: the difference between the categories of “superior” and “average” intelligence—or more pointedly, from “average” to “borderline deficient.” That’s a greater deficit than subjects in sleep studies typically show after staying awake for 24 hours, Mullainathan and Shafir highlight. “Simply raising monetary concerns for the poor,” they explain, “erodes cognitive performance even more than being seriously sleep deprived.”
They attribute this result to the maelstrom of problems poor people must suddenly confront in the face of a large unexpected expense: how will I pay the rent, buy food, take care of my kids? This round of mental juggling depletes the amount of mental bandwidth available for everything else. Such problems simply don’t arise for the rich.
To rule out other factors, the researchers posed nonfinancial questions with small and large numbers; they even tried versions where they paid people for correct answers to questions. In each case, there was no difference in performance.
But the real test lay in the real world, Mullainathan continues. If just thinking about scarcity preoccupied subjects, what effect would real scarcity have?
The answer came from fieldwork he and his colleagues were already conducting in India. Sugarcane farmers, they discovered, get their income in one lump sum at harvest time, just once or twice a year. That meant farmers were poor during one part of the year, and flush with cash during another. Because harvests took place at different times for different farmers, researchers could rule out seasonal weather, events, and their accompanying obligations as bandwidth-usurping factors. And when the researchers conducted a study there similar to the New Jersey mall experiment, the results mirrored their original findings: the Indian farmers performed worse on Raven’s Matrices tests before their harvest, and better after they’d been paid.
The conclusion was clear, Mullainathan explains: poverty itself taxes the mind. And in the case of the Indian farmers, he adds, the data were even more convincing: unlike the New Jersey “lab” study, where subjects were compared to other people, the farmers were compared to themselves. The only variables that had changed were their financial circumstances.