Many advocates for daylight savings time claim that it saves money by reducing energy consumption. Generally it would be hard to run an experiment to test this claim, but as fortune would have it, counties in Indiana provided an opportunity. Until 2006, only 15 of the 92 counties in Indiana used daylight savings time. The rest had remained on standard time. Now all are on daylight savings time. The local energy provider has access to utility records in counties that recently moved to daylight savings time and counties that did not. How can it exploit these data to test the benefits of daylight savings time?