A good nudge is like a GPS device: A small, low-cost intervention that tells you how to get where you want to go — and if you don’t like what it says, you’re free to ignore it. But when, exactly, will people do that? A new study sheds important light on that question, by showing the clear limits of nudging. Improbably, this research is also good news: It shows that when people feel strongly, it’s not easy to influence them to make choices that they won’t like.

The focus of this new research, as with much recent work on behavioral science, is on what people eat. Numerous studies suggest that if healthy foods are made more visible or convenient to find, more people will choose them. We tend to make purchasing decisions quickly and automatically; if certain foods or drinks — chocolate bars, apples, orange juice — are easy to see and grab, consumption will jump.

At a University of Pennsylvania salad bar, for example, researchers found that moving high-calorie foods like cheese just 25 cm farther away reduced intake of those foods as much as 16 percent. In another study, at the cafeteria in Boston’s Massachusetts General Hospital, placing salads next to the pizza counter and putting green items at eye level nudged people to buy healthier food.

But new research shows there are limits to how much the placement of food can influence what people choose. A team led by Rene A. de Wijk of the Wageningen University & Research Center in the Netherlands sought to increase consumption of whole-grain bread, which is generally healthier than other kinds of bread. For several weeks, they placed the whole-grain bread at the entrance to the bread aisle — the most visible location. And for different weeks, they placed it at the aisle’s exit (the least visible location).

Behavioral science makes a confident prediction: When whole-grain bread is more visible, more people will buy it. In advance, you might not be sure about the precise size of the effect, but it will be significant. Except there was no effect! Whole grain accounted for about one-third of the bread sold — and it didn’t matter whether it was encountered first or last.

As the authors suggest, the best explanation for their finding is that people know what bread they like, and they’re going to choose it, whatever the architecture of the supermarket. Some like the taste of white bread; while they may know whole grain is healthier, they won’t select it, even if it’s staring them in the face. And because health-conscious consumers prefer whole grain, that’s what they’ll get, whether it’s at the entrance or the exit.

They can’t be nudged. Interestingly, people’s desire for one or another kind of bread appears to be very strong — stronger than their desire for other kinds of food (such as salad or cheese), where nudging has been found to work.

The finding by de Wijk and his colleagues is the latest contribution to a growing body of work on ineffective nudging. Workers are usually influenced by the default savings rate that employers choose for their pension plans, but if employers make the savings rate very high (say, 12 percent), most employees are going to opt out. If employers turn down the default setting on office thermostats by 1 degree, they’ll probably save real money; but turn them down 2 degrees and they’ll save much less, because people will get cold and turn the temperature up again. People are usually influenced by social norms, but if you inform smokers that the vast majority of Americans don’t smoke, they won’t suddenly quit.

For anyone who wants to change behavior, there’s a cautionary note here: If people have strong preferences, they’re far less likely to be nudge-able. True, that means that there can be real constraints on the power of nudges to produce change. But in a way, that’s excellent news.

It’s perfectly legitimate for governments and private institutions to help people to achieve their own goals, or to act in accordance with their aspirations. (The life you save might be your own.) But if you want to go your own way, you’re usually allowed to do so. When a nudge doesn’t work, we should not mourn — because its very failure is a tribute to freedom’s ultimate authority. It’s a good reminder: Small features of the social environment can have big effects on our actions, but we are hardly automatons, and if we know exactly what we want, we’ll probably choose it.

Cass R. Sunstein is the Robert Walmsley university professor at Harvard Law School and a Bloomberg View columnist.

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