Using less energy saves money and lowers greenhouse gas emissions. And various studies have looked at ways to get households to use less energy. Now there's evidence that people in such a study use less energy...because they're in a study. The general phenomenon is called the Hawthorne effect: study subjects change their behavior because they're being observed. So researchers collaborated with a utility to test for the Hawthorne effect in electricity use. They monitored almost 5,600 randomly selected households. Half received a postcard saying that their energy use would be monitored for a month for research purposes. They also got four follow-up reminder postcards over the month. They received no other information, instructions or incentives. The control group monitored for the study got no notifications. That group continued using the same amount of electricity. But the families being tracked reduced energy use 2.7 percent. And when the study period ended, their energy use shot back up.