"If you do something good, there have been lab studies showing that you will reward yourself, even if the reward is not related to the good act," says Bryan Bollinger. (Credit: Peter Gerdes/Flickr)

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Do reusable bags trick you into buying junk food?

Bringing reusable bags to the grocery store might make you feel like you deserve a yummy reward.

A new study suggests shoppers who use reusable bags not only buy more environmentally friendly products, they buy more indulgent ones, too.

“If you do something good, there have been lab studies showing that you will reward yourself, even if the reward is not related to the good act,” says Bryan Bollinger, assistant professor of marketing at Duke University.

“It’s known as the licensing effect. We were curious whether bringing your own bag might license you to indulge yourself with unhealthy food.”

More ice cream and chips

“There had been a push in California for people to start using their own bags, so we started thinking about whether there could be any other consequences of incentives to do that,” Bollinger says.

For the study, published in the Journal of Marketing, researchers studied receipts from a California supermarket between 2005 and 2007, spanning more than 2 million transactions by almost 60,000 households. The loyalty card transaction data noted a small discount when shoppers brought their own bags.

“We could look at how the same shopper behaved on occasions when he or she did bring a bag versus the times he or she did not,” Bollinger says. “So the effect we’re capturing is not about differences across consumers, it’s all comparing choices made by the same consumer on different occasions.”

The researchers examined the habits of 884 families who made almost 143,000 shopping trips during the two-year study period. They found shoppers who brought their own bags were more likely to buy organic goods, but also more likely to pick up indulgent items, like ice cream, cakes, candy, cookies, and chips.

Indulge yourself

The researchers also tested their hypothesis in the lab with 111 participants.

“We told people they were in a shopping environment, and some were randomly told that they had put their reusable bags inside the shopping cart,” Bollinger says. “We asked them an open-ended question about what items they might purchase. They were more likely to buy indulgent items when they had their reusable grocery bags inside their cart.”

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Shoppers listed twice as many indulgent items when they were told they had brought their own bag. But the lab study also showed why they were using a reusable bag mattered as well.

“In one condition the shopper was told they brought it, in another we had the store require it,” Bollinger says. “The licensing effect completely went away in that second scenario. You really only indulge yourself when you’re the impetus to bring the bags.”

The findings could be significant to store managers in the placement of products and encouraging shoppers to bring their own bags.

“But it can’t feel like the store is forcing shoppers to bring bags. You have to make them feel like it was their idea.”

Uma Karmarkar of Harvard Business School is coauthor of the study.

Source: Duke University

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