than borrow to invest as firms typically do. Corporate investment, a key demand component of GDP, fell enormously (22% of GDP) between 1990 and its peak decline in 2003. Japanese firms overall became net savers after 1998, as opposed to borrowers. Koo argues that it was massive fiscal stimulus (borrowing and spending by the government) that offset this decline and enabled Japan to maintain its level of GDP. In his view, this avoided a U.S. type Great Depression, in which U.S. GDP fell by 46%. He argued that monetary policy was ineffective because there was limited demand for funds while firms paid down their liabilities. In a balance sheet recession, GDP declines by the amount of debt repayment and un-borrowed individual savings, leaving government stimulus spending as the primary remedy. Krugman discussed the balance sheet recession concept in 2010, agreeing with Koo's situation assessment and view that sustained deficit spending when faced with a balance sheet recession would be appropriate. However, Krugman argued that monetary policy could also affect savings behavior, as inflation or credible promises of future inflation (generating negative real interest rates) would encourage less savings. In other words, people would tend to spend more rather than save if they believe inflation is on the horizon. In more technical terms, Krugman argues that the private sector savings curve is elastic even during a balance sheet recession (responsive to changes in real interest rates), disagreeing with Koo's view that it is inelastic (non-responsive to changes in real interest rates). A July 2012 survey of balance sheet recession research reported that consumer demand and employment are affected by household leverage levels. Both durable and non-durable goods consumption declined as households moved from low to high leverage with the decline in property values experienced during the subprime mortgage crisis. Further, reduced consumption due to higher household leverage can account for a significant decline in employment levels. Policies that help reduce mortgage debt or household leverage could therefore have stimulative effects. Liquidity trap A liquidity trap is a Keynesian theory that a situation can develop in which interest rates reach near zero (zero interest-rate policy) yet do not effectively stimulate the economy. In theory, near-zero interest rates should encourage firms and consumers to borrow and spend. However, if too many individuals or corporations focus on saving or paying down debt rather than spending, lower interest rates have less effect on investment and