Diane Coyle, professor at the University of Manchester with a PhD in economics from Harvard, is one of the internationally renowned scholars in the debate on how we best define and measure national economies. She has authored a number of books, the latest one titled GDP: A Brief but Affectionate History (Princeton University Press). The book explains why even small changes in GDP can influence major political decisions and determine whether countries can keep borrowing or be thrown into recession. Coyle makes the case that GDP was a good measure for the twentieth century but is increasingly inappropriate for a twenty-first-century economy driven by innovation, services, and intangible goods.