The economy of the Unite States is the world's largest national economy. Its gross domestic product (GDP) was estimated as $13.8 trillion in 2007. It is a mixed economy and private firms that make the majority of the microeconomic decisions, while being regulated by the government. The U.S. economy maintains a high level of output per person (GDP per capita, $46,000 in 2007, ranked within the top ten highest by most sources). The U.S. economy has maintained a stable overall GDP growth rate, a low unemployment rate, and high levels of research and capital investment. Major economic concerns in the U.S. include national debt, external debt, entitlement liabilities for retiring baby boomers who have already begun entering the Social Security system, corporate debt, mortgage debt, a low savings rate, and a large current account deficit. In 2008, seventy-two percent of the economic activity in the U.S. came from consumers.