Bringing your own reusable bags to the grocery store is a very good thing for the environment, as (obviously) it’s less wasteful than coming home with an armload of plastic bags you’re either going to throw away or stuff under your sink and forget about. The only problem, perhaps, is that we know it’s a very good thing we’re doing — and as such, researchers at Harvard Business School report in a new working paper, we reward ourselves by buying more junk food.
Using about two years’ worth of customer loyalty-card data from one location of a California grocery-store chain, Uma R. Karmarkar and Bryan Bollinger analyzed nearly 1 million transactions. The store offered a small discount when shoppers brought reusable bags, and it was marked on each receipt, allowing the researchers to tell who was bringing their own bags. (They excluded purchases that weren’t typical weekly shopping trips — late-night visits to the store, for example, and transactions with only one or two items.)
After analyzing the transactions, Karmarkar and Bollinger found small but statistically significant trends associated with bringing reusable bags. First, those with reusable bags were slightly more likely — 0.25 percent — to buy organic basics like milk and eggs. One green behavior may provide a gentle nudge into another, the researchers conclude. But those who brought their own bags were also slightly more likely — 1.24 percent — to buy indulgent (nonorganic) items, like potato chips and candy.
These are not huge numbers, and Karmarkar acknowledges that the results may have been different if the data were gathered from another location, like the East Coast. Still, it’s an example of what consumer psychologists call licensing — following a bit of good behavior with a bit of bad behavior.
“Similar research has also been done on health decisions. I get a Diet Coke; I treat myself to a hamburger,” Karmarkar told Harvard Business Review. “In this case bringing a bag makes you think you’re environmentally friendly, so you get some ice cream. You feel you’ve earned it.” In other words, she said, bring your own bag to the store, and you may literally reward yourself with a cookie.