DAVID GREENE, HOST:
You know, before coming into the studio this morning, I stopped at a grocery store and I was checking out, and they charged me 5 cents for using a plastic bag because Washington, D.C., is trying to reduce the use of plastic bags. And I saw other people not paying this price. They had their reusable bags, which more and more people are doing. It's good news for the environment, maybe not good news, though, for people. And NPR social science correspondent Shankar Vedantam is here to explain why. Hey, Shankar.
SHANKAR VEDANTAM, BYLINE: Hi, David.
GREENE: How can using reusable bags be bad?
VEDANTAM: Well, in some ways, I think, David, it's a wonderful example of how complicated human behavior can be, where you're doing something in one domain that makes total sense but it can have unintended consequences in another domain. Uma Karmarkar at the Harvard Business School and Bryan Bollinger, they analyzed purchases made by shoppers at a very large California grocery store, and they find two things, one of which makes intuitive sense and one of which is very counterintuitive.
GREENE: OK.
VEDANTAM: Customers who bring in these reusable bags tend to buy more environmentally conscious food. They buy more organic food. And, of course, that makes intuitive sense to me. But they also buy more junk food. They buy more candy, and they buy more potato chips.
GREENE: I mean, is it possible that people who just shop for potato chips happen to be the people who would then...
VEDANTAM: (Laughter).
GREENE: ...Decide to use reusable bags somehow? Or - what's the link here or the causation?
VEDANTAM: So what they found right now is just a correlation. It could be that people who like potato chips and cookies prefer to use reusable bags for some reason. So the researchers ran a couple of experiments, which suggest that when people visualize taking their own bags to get groceries, especially when they are doing it of their own accord and not because of a store policy, they're more likely to indulge themselves and buy themselves treats.
GREENE: OK, which leads us to the question of why, if you're using reusable bags, it would make it more likely that you would want to eat bad food.
VEDANTAM: Yeah, so there's been a lot of work looking at an idea called licensing, David. When people feel they're doing something hard or something virtuous, they often give themselves license to do something that rewards themselves. So I go to the gym, I work out, and then I tell myself, look, that entitles me now to an ice cream sundae. The same thing might be happening here with grocery bags. Consumers who are doing the environmentally responsible thing might hear a little voice at the back of their heads that say, look, you're such a good human being, you deserve a little treat.
GREENE: Shankar, talking to you is so easy, I am entitled to nothing because of this. I appreciate that.
VEDANTAM: (Laughter) You're welcome, David.
GREENE: Thanks, Shankar. Transcript provided by NPR, Copyright NPR.
