"Virtue," according to George Ber-V nard Shaw, "is insufficient temptation." But new research on the consumption patterns of the environmentally minded suggests that virtue and self-indulgence often go hand-in-hand. A recent paper* by Uma Karmarkar of Harvard Business School and Bryan Bollinger of Duke Fuqua School of Business finds that shoppers who bring their own bags when they buy groceries like to reward themselves for it. For two years the authors tracked transactions at a supermarket in America. Perhaps unsurprisingly, shoppers who brought their own bags bought more green products than those who used the store's bags. But the eco-shoppers were also more likely to buy sweets, ice cream and crisps.
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