New York Times: In an era of climate change and expensive gasoline, a vehicle’s fuel efficiency, measured in miles per gallon, is an increasingly important factor to consider when shopping for a car. But two Duke University business school professors say m.p.g. is a flawed measure and leads to a fundamental misconception about efficiency. They say the United States should do what some other countries do, which is rate cars by amount of fuel consumed for a given distance, gallons per 100 miles, for …