Contributor(s): Professor Diane Coyle | Why did the size of the U.S. economy increase by 3 percent on one day in mid-2013—or Ghana's balloon by 60 percent overnight in 2010? Why did the U.K. financial industry show its fastest expansion ever at the end of 2008—just as the world's financial system went into meltdown? And why was Greece's chief statistician charged with treason in 2013 for apparently doing nothing more than trying to accurately report the size of his country's economy? The answers to all these questions lie in the way we define and measure national economies around the world: gross domestic product. Diane Coyle (@diane1859) is professor of economics at the University of Manchester. She runs the consultancy Enlightenment Economics, and as well as a regular blog, she is the author of numerous books, including The Economics of Enough and The Soulful Science: What Economists Really Do and Why It Matters. Her latest book is GDP: A Brief but Affectionate History. The Department of Economics at LSE (@LSEEcon) is one of the largest economics departments in the world. Its size ensures that all areas of economics are strongly represented in both research and teaching. The Centre For Macroeconomics (@CFMUK) brings together world-class experts to carry out pioneering research on the global economic crisis and to help design policies that alleviate it.