Mullainathan worked with a bank in South Africa that wanted to make more loans. A neoclassical economist would have offered simple counsel: lower the interest rate, and people will borrow more. Instead, the bank chose to investigate some contextual factors in the process of making its offer. It mailed letters to 70,000 previous borrowers saying, “Congratulations! You’re eligible for a special interest rate on a new loan.” But the interest rate was randomized on the letters: some got a low rate, others a high one. “It was done like a randomized clinical trial of a drug,” Mullainathan explains.
The bank also randomized several aspects of the letter. In one corner there was a photo—varied by gender and race—of a bank employee. Different types of tables, some simple, others complex, showed examples of loans. Some letters offered a chance to win a cell phone in a lottery if the customer came in to inquire about a loan. Some had deadlines. Randomizing these elements allowed Mullainathan to evaluate the effect of psychological factors as opposed to the things that economists care about—i.e., interest rates—and to quantify their effect on response in basis points.
“What we found stunned me,” he says. “We found that any one of these things had an effect equal to one to five percentage points of interest! A woman’s photo instead of a man’s increased demand among men by as much as dropping the interest rate five points! These things are not small. And this is very much an economic problem. We are talking about big loans here; customers would end up with monthly loan payments of around 10 percent of their annual income. You’d think that if you really needed the money enough to pay this interest rate, you’re not going to be affected by a photo. The photo, cell phone lottery, simple or complicated table, and deadline all had effects on loan applications comparable to interest. Interest rate may not even be the third most important factor. As an economist, even when you think psychology is important, you don’t think it’s this important. And changing interest rates is expensive, but these psychological elements cost nothing.”
Mullainathan is helping design programs in developing countries, doing things like getting farmers to adopt better feed for cows to increase their milk production by as much as 50 percent. Back in the United States, behavioral economics might be able to raise compliance rates of diabetes patients, who don’t always take prescribed drugs, he says. Poor families are often deterred from applying to colleges for financial aid because the forms are too complicated. “An economist would say, ‘With $50,000 at stake, the forms can’t be the obstacle,’” he says. “But they can.” (A traditional explanation would say that the payoff clearly outweighs the cost in time and effort, so people won’t be deterred by complex forms.)
Thanks to a reader — his name mistakenly deleted from my email — for the pointer.