How Grocery Bags Manipulate Your Mind

People who bring personal shopping bags to the grocery store to help the environment are more likely to buy organic items—but also to treat themselves to ice cream and cookies, according to new research by Uma R. Karmarkar and Bryan Bollinger. What's the Quinoa-Häagen-Dazs connection?
by Carmen Nobel

There's a classic cartoon plot device that represents a struggle with temptation. A tiny angel pops up on the conflicted character's left shoulder, urging him to follow the path of righteousness. A tiny devil sits on his right shoulder, pressing him to give into his desires.

In real life, it turns out that an everyday item has the power to act as both angel and devil every time we go to the grocery store. It lurks in car trunks and pantries all over the world, waiting to guide us simultaneously down paths of virtue and vice. What is this surprising Svengali?

It's a reusable shopping bag.

“You did something good for the environment, so you can have a cookie.”

New experimental research shows that shoppers are more likely to buy virtuous organic items when they bring their own reusable bags to the store than when they opt for paper or plastic bags at the checkout counter. At the same time, those who bring their own bags are more likely to buy indulgent items like ice cream and cookies. Moreover, consumers tend to place a higher value on both organic products and decadent treats when they bring their own bags than when they don't.

Researchers Uma R. Karmarkar and Bryan Bollinger report their preliminary findings in their working paper BYOB: How Bringing Your Own Shopping Bags Leads to Treating Yourself, and the Environment. (The collaborative effort addresses each of their particular interests. Karmarkar, an assistant professor and neuroscientist in the Marketing unit at Harvard Business School, studies factors that affect consumer choice. Bollinger, an assistant professor at NYU's Stern School of Business, studies the marketing of sustainable products.)

"There are all these little things that we're supposed to do to be better to the environment, like turning off the lights when we leave the room or recycling our bottles," Karmarkar says. "Bringing bags is interesting in that it's a difficult thing to remember to do, and actually requires a fairly big behavioral change on the part of the consumer. Our question was, when you succeed at this big behavioral change, does it change other elements of what you're doing as well?"

A Series Of Experiments

As their working paper explains, the researchers combined empirical and experimental methods to test the purchasing effect of reusable bags.

Using reusable bags increases our tendency to buy both organic and indulgent items.
Photo: iStockPhoto

Looking at loyalty card data from a large grocery chain in California, Karmarkar and Bollinger tracked and analyzed 936,232 purchases by 5,987 households across two years. To assess organic purchases, they looked for transactions in which the consumer could choose either an organic or a nonorganic option—a carton of milk, for example. In monitoring what they called "indulgent" purchases, the researchers looked at sugary items like ice cream and candy bars, as well as salty treats like potato chips.

The data showed a definite correlation: Shoppers who had brought their own bags bought decidedly more indulgences and chose more organic products than those who didn't. But this wasn't necessarily enough information to establish causality—that is, that both effects were specifically due to bringing their own bags. "There are a lot of things going on in a store and a lot of inputs," Karmarkar says.

So she and Bollinger dug deeper with a series of experiments, enlisting participants for a number of online surveys.

In the first experiment, the researchers assigned participants to one of two conditions. The "with bags" participants were asked to imagine approaching a supermarket to do their grocery shopping with their own bags. The "without bags" group received nearly identical instructions, but nothing about bags was mentioned. All the participants looked at a floor map of the grocery store and listed 10 items they would most likely purchase on their hypothetical outing.

Regarding indulgent items, the results depended on whether the participants had children in their households. For those with dependents, there was no significant difference between the with-bags and the without-bags condition. For those without children, the with-bags participants were more likely to imagine buying ice cream and potato chips than the -without-bags- participants.

But the results couldn't speak to organic items; while participants listed items such as milk and vegetables, they generally didn't list whether their hypothetical choices were organic milk and vegetables.

"We could support some of the story but not all of it yet," Karmarkar says.

And so she and Bollinger conducted a second experiment, in which participants reported how much they'd be willing to pay for each of nine specific products. These included both organic and indulgent items, as well as "baseline" items like canned soup. Again, the participants were divided into hypothetical conditions of "with bags" and "without bags."

Consistent with the empirical data, the idea of bringing their own bags increased the likelihood that participants would buy both indulgent and organic items. Moreover, it increased the amount of money they'd be willing to pay for those items.

But the researchers had another question: Does it matter whether a reusable bag is the consumer's choice? "We wanted to examine whether it was important that you made the decision to bring the bags as opposed to a store policy that requires it," says Karmarkar, noting that some stores obligate customers to bring their own bags; others charge customers a fee for single-use carryout bags per a local government mandate.

In the next experiment, all the participants imagined bringing their own bags to the hypothetical grocery store. But while some were told to imagine bringing reusable bags of their own volition, others imagined that they had to bring bags due to a store policy.

Participants then rated their willingness to purchase organic, indulgent, and baseline items. In this case, the results showed no significant difference between the two groups with regard to organic items, which rated highly across the board. However, participants were more likely to buy indulgent foods if they imagined that bringing bags was their own choice.

"A simple way I think about those results is that if you do something good, you reward yourself," Karmarkar says. "You did something good for the environment, so you can have a cookie."


For retailers, the results suggest that store managers should reconsider where they display their organic items. In short, it may make sense to locate the kale near the Kit Kats.

"The research implies that the area near the checkout counter is a good place to display organic or environmentally positive items," Karmarkar says. "That's the place where shoppers' attention is probably going to be most focused on this element, the bag, which seems to encourage them to buy these things."

For consumers, she recommends that they just think about the findings as they stroll down the grocery store aisles.

"I'm of the mindset that it's useful to know the kinds of things that influence your own behavior," Karmarkar says. "If you're trying to maintain a strict diet, maybe you can recognize the bag's influence, and consciously fill the desire to treat yourself in another way that doesn't interfere with your goals. Maybe you can treat yourself to an extra half hour of sleep."

About the Author

Carmen Nobel is the senior editor of Harvard Business School Working Knowledge.
    • Cate
    • Marketing
    I'm wondering if instead of a "reward" phenomenon going on here may be it's one of "disposable income"?
    • Pat
    Hmmm.... One wonders why such research is even done. For example, I bring my own re-usable bag -- when the store rewards me for doing so (e.g., points or 5 cents off). I buy organic products when possible -- ever read Life Over Cancer or Anti-Cancer (two excellent books). I also grow some of my own food, using "quasi-organic" methods -- it wouldn't meet the government's definition, but no pesticides, etc. And I never treat myself to ice cream cones or cookies. What does that say about the research? Were there perhaps variables that were not considered? But, again, why was this research even conducted?
    • Matthew G
    • Designer, MDB
    "In the first experiment, the researchers assigned participants to one of two conditions. The 'with bags' participants were asked to imagine approaching a supermarket to do their grocery shopping with their own bags. The "without bags" group received nearly identical instructions, but nothing about bags was mentioned. All the participants looked at a floor map of the grocery store and listed 10 items they would most likely purchase on their hypothetical outing."

    Participants were asked to *imagine* having bags on a *hypothetical* grocery shopping trip? How far removed from reality did you want this study to be?

    To do a proper experiment of this sort you need to have participants actually grocery shopping in their normal routine.
    They need to be choosing whether or not to bring a bag on their own.
    They need to look at actual grocery shelves with prices and make decisions in real time.
    They should ideally not even know they're being studied (which you achieved in the first experiment using store data, but failed to do in the follow ups).
    • AlanG
    • Manager, JCR
    Reminds me somewhat of the Peltzman Effect.
    • Susan Chipman
    • retired
    As is too often the case with behavioral studies reported in this newsletter, this is a very weak study that I would not recommend for publication if I were professionally reviewing it.
    In my opinion, people who bring in shopping bags are likely to be different in the first place and that possibility has not been ruled out.
    It seems to me that it probably could be, given cooperation from a grocery store with good computer records. I currently live in Boulder, CO where the law requires a charge for grocery bags, credit being given if the customer brings in bags. So one could test for differences in purchase behavior when the same individual (identified by store discount cards) does or does not remember to bring in bags.
    "Imagining" such circumstances is a very weak manipulation that probably should not be taken seriously.

    MBA 1967, PhD Experimental Psychology 1973
    • Sridevi Saravanan
    • Associate Professor, Sri Krishna Institute of Management
    Excellent and a practical research work. Implications are relevant to all the stake holders of today's environment.
    • Marcia Mogelonsky
    • Director of Insight, Mintel
    I do not consider this to be a complete piece of research; the findings are questionable and the methodology is unreliable. Imagining a shopping trip is a different experience than being in a supermarket, and the results of an imagined shopping mission are always going to be different from the reality of a run through an actual store. I do think that the study opens up an area worth considering - does the bag influence the purchase? But, I would submit that there are other factors worth considering besides an ill defined reward pattern. Does the logo on the reusable bag make a statement about the shopper? Does the size of the bag affect purchase patterns (bigger bags can be heavier, so do shoppers buy less?) What about how many bags - do shoppers choose products based on availability of reusable bags or do they "give up" at the end and go for the hybrid "some of mine, some of the store's?).

    I think that the idea of testing the influence of reusable bags is good; I just don't agree with the consequences the researchers chose to focus on.
    • Dr.S.P.Thenmozhi
    Interesting article.
    • Kapil Kumar Sopory
    • Company Secretary, SMEC(India) private Limited
    This piece of research is interesting but on the face of it of academic interest only. My experience is that prefence for organic items is not in direct proportion BYOB habit. People generally bring their own bags as the larger outlets discourage providing their bags by charging cost of the bag supplied. Moreover, people want to use their own bags - plastic or any other - till these reach a stage of disuse. Environmental concerns are emphasised at government levels but appreciation at ground level has not developed well.
    Plastic bags, though almost banned, are still in use and mechanism for regulating these guidelines is still somewhat weak.
    • Anonymous
    For those of us who embrace the mindset that we all have a role to play, however modest, in securing a safer, cleaner future for our children, the conclusions of this study have real value. We (and our growing population of like thinkers) do take pride in placing our reusable shopping bags on the conveyer belt, along with our purchases. And the large grocery chains are providing the "hardware" to make it easier for cashiers to load our purchases into these variously-sized bags. The self-rewarding with organic cookies, etc. (can you say, "Newman's Own"?) is an observation which is right on the money. Marketers would do well to honor this finding, and replace the plethora of pure junk in the checkout aisles with organically-based, equally delicious (often higher priced) treats.
    • Shelley
    Is this relevant in South Africa where for many years we have paid for grocery bags?

    I personally buy relatively durable bags which support good causes or use those handed out as corporate gifts. This applies to most of my friends and family. We don't see using reusable bags as "good" - just a way of life.
    • chandler hadraba
    • Founder | Principal, Shopping Bag Solutions
    Outstanding article, and as a successful litigant against the State of California on Plastic Bags, I can also tell you that the Grocery stores would prefer you to keep "forgetting" your bags and charging you each time, and charge you even more for reusable bags, 90% of which are made in China. And you, eco-fashist organic shopper, the fact your bag is made in a 3rd world nation under the guise of "fair trade", is the most brilliant marketing scam ever. I make a product right here in America, by disabled Vets, and help create new jobs, paying wages to live here, do your purchases support this kind of sustainability?
    It is time that both tech and the Organic foods movement actually lead to job creation here, and quit sounding like the corporate crooks on Wall St, motivated only by profit.
    Imagine if we could return to the times when there was so much economic opportunity, the huddled masses can come out of the shadows and be welcomed into the labor force.
    What is also left out of this debate is the on-line behavior of shopping cart abandonment, actually happening in the real world. People will walk away from a purchase due to not receiving a code or discount, and this behavior is happening in the real world. Forgetting your bag is truly a "disruptive event", and having the UX or CX be disruptive is bad for business.
    • Perry
    • Sheridan, Independent Marketing Consultant
    This research is really weak. As pointed out by some of the comments, imagining is not real shopping.To get at this, the researchers must use real shopping situations.
    In the first study, the shoppers who get the recyclable bags and those who do not are very likely different customers who espouse different values etc.
    The study may be strengthened by looking at the same customers under different conditions using real shopping situations. Also customers in the different studies used in this research are not the same customers.

    And the implications of the study are impractical. As a consultant to grocery and other stores, I can say with confidence that a lot of factors go into the location of products in a store. So to say that "In short, it may make sense to locate the kale near the Kit Kats" is erroneous.