His most outstanding contribution to economic theory was the joint development, with
John Hicks, of the so-called
IS–LM model, also known as the "Hicks–Hansen synthesis." The IS–LM diagram claims to show the relationship between the
investment-
saving (IS) curve and the
liquidity preference-
money supply (LM) curve. It is used in
mainstream economics literature and textbooks to illustrate how monetary and fiscal policy can influence GDP. Hansen's book of 1938,
Full Recovery or Stagnation. based in Keynes's
General Theory, presents his thesis for both growth and employment being stagnant if there is no economic state intervention to stimulate
demand. Hansen presented evidence on several occasions before the
U.S. Congress to oppose the use of
unemployment as the main means of fighting
inflation. He advocated instead that inflation could be controlled by changes in interest- and tax-rates as well as controls on prices and wages. Lately, theories of economic stagnation have become more associated with Hansen's ideas than with those of Keynes.
Keynesianism Hansen, in his review of
The General Theory of Employment, Interest and Money, was skeptical of
John Maynard Keynes's propositions, but by December 1938, in his presidential address to the
American Economic Association, he embraced Keynesian theories of the need for government intervention in periods of economic recession. Soon after his arrival at Harvard in 1937, Hansen's famous graduate seminar on fiscal policy began inspiring graduate students such as
Paul Samuelson and
James Tobin (both of whom would go on to win the
Economics Nobel) to further develop and popularize Keynesian economics. Hansen's 1941 book,
Fiscal Policy and Business Cycles, was the first major work in the United States to entirely support Keynes's analysis of the causes of the
Great Depression. Hansen used that analysis to argue for Keynesian
deficit spending. Hansen's best known contribution to economics was his and
John Hicks's development of the
IS–LM model, also known as the "Hicks–Hansen synthesis." The framework claims to graphically represent the investment-savings (IS) curve and the liquidity-money supply (LM) curve as an illustration of how fiscal and monetary policies can be employed to alter national income. Hansen's 1938 book,
Full Recovery or Stagnation, was based on Keynesian ideas and was an extended argument that there would be long-term employment stagnation without government demand-side intervention.
Paul Samuelson was Hansen's most famous student. Samuelson credited Hansen's
Full Recovery or Stagnation? (1938) as the main inspiration for his famous
multiplier-accelerator model of 1939. Leeson (1997) shows that while Hansen and
Sumner Slichter continued to be regarded as leading exponents of Keynesian economics, their gradual abandonment of a commitment to price stability contributed to the development of a Keynesianism that conflicted with positions of Keynes himself.
Stagnation In the late 1930s, Hansen argued that "secular stagnation" had set in so the American economy would never grow rapidly again because all the growth ingredients had played out, including technological innovation and population growth. The only solution, he argued, was constant, large-scale deficit spending by the federal government. The thesis was highly controversial, as critics, such as George Terborgh, attacked Hansen as a "pessimist" and a "defeatist." Hansen replied that secular stagnation was just another name for Keynes's underemployment equilibrium. However, the sustained economic growth, beginning in 1940, undercut Hansen's predictions and his stagnation model was forgotten.
Economic cycles One of the most important contribution to the economic theory by Alvin Hansen are the economic cycles. In his book
Business Cycles and National Income, he defines the cycle as a fluctuation in: employment, output, and prices. The cycle is divided in two phases: expansion, extending from trough to peak; and contraction, extending from peak to trough. For Hansen, there exist stable and unstable economic cycles. The instability is caused by displacement due to external shocks. Hansen claims that the business-cycle analysis must take into consideration technical progress, the money market, and expectations. ==Public policy==