change in the national debt were significantly different. For example, the U.S. added $1trillion to the national debt in FY2008 but reported a deficit of $455billion. Due to rules changes implemented under President Obama in 2009, the two figures have moved closer together and were nearly identical in 2013 (a CBO-reported deficit of $680billion versus change in debt of $672billion). For FY2014, the difference widened again, with the CBO reporting a deficit of $483billion compared to a change in total debt outstanding of $1,086billion. Debt categories The total federal debt is divided into "debt held by the public" and "intra-governmental debt." The debt held by the public refers to U.S. government securities or other obligations held by investors (e.g., bonds, bills, and notes), while Social Security and other federal trust funds are part of the intra-governmental debt. As of September 30, 2012, the total debt was $16.1trillion, with debt held by the public of $11.3trillion and intragovernmental debt of $4.8trillion. Debt held by the public as a percentage of gross domestic product (GDP) rose from 34.7% in 2000 to 40.3% in 2008 and 70.0% in 2012. U.S. GDP was approximately $15trillion during 2011 and an estimated $15.6trillion for 2012 based on activity during the first two quarters. This means the total debt is roughly the size of GDP. Economists debate the level of debt relative to GDP that signals a "red line" or dangerous level, or if any such level exists. By comparison, China's budget deficit was 1.6% of its $10trillion GDP in 2010, with a debt to GDP ratio of 16%. Risks associated with the debt The CBO reported several types of risk factors related to rising debt levels in a July 2010 publication: A growing portion of savings would go towards purchases of government debt, rather than investments in productive capital goods such as factories and leading to lower output and incomes than would otherwise occur; Rising interest costs would force reductions in important government programs; To the extent that additional tax revenues were generated by increasing marginal tax rates, those rates would discourage work and saving, further reducing output and incomes; Restrictions to the ability of policymakers to use fiscal policy to respond to economic challenges; and An increased risk of a sudden fiscal pressure on the government, in which investors demand higher interest rates. However, since mid- to late-2010, the U.S. Treasury has been obtaining negative