In the journal Environment and Behavior, French and Italian researchers describe an experiment in which they asked people entering a Paris supermarket to sign a poster reading, “Stop using plastic bags. If I can do it, so can you.” Half of those who signed were then asked whether they ever used the environmentally problematic containers; they all admitted to doing so at least occasionally. The other half weren’t asked any such follow-up question. Later, at the checkout line, researchers compared the actions of all signers to those of a third group who had not been asked to do anything. Relative to the control group, the people who had simply signed the poster, with no follow-up question, were more likely to buy a reusable bag than take a free plastic one. The signers who were asked the question, however, used plastic bags at the same rate as the control group.
The researchers theorize that somewhere between the produce aisle and the cash register, those shoppers who had confessed their previous plastic transgressions found a way to justify their past behavior, and thus felt no need to change it.