In monetarist economics, particularly the work of Milton Friedman, NAIRU is an acronym for non-accelerating inflation rate of unemployment, and refers to a level of unemployment below which inflation rises. It is widely used in mainstream economics. It was also introduced as NIRU (non-inflationary rate of unemployment) in Modigliani – Papademos (1975).
An early form of NAIRU is found in the work of Abba P. Lerner (Lerner 1951, Chapter 14), who referred to it as "low full employment" attained via the expansion of aggregate demand, in contrast with the "high full employment" which adds incomes policies (wage and price controls) to demand stimulation.
The concept arose in the wake of the popularity of the Phillips curve which summarized the observed negative correlation between the rate of unemployment and the rate of inflation (measured as annual nominal wage growth of employees) for number of industrialised countries with more or less mixed economies. This correlation (previously seen for the U.S. by Irving Fisher) persuaded some analysts that it was impossible for governments simultaneously to target both arbitrarily low unemployment and price stability, and that, therefore, it was government's role to seek a point on the trade-off between unemployment and inflation which matched a domestic social consensus.
During the 1970s in the United States and several other industrialized countries, Phillips curve analysis became less popular, because inflation rose at the same time that unemployment rose (see stagflation).
Worse as far as many economists were concerned, the Phillips curve had little or no theoretical basis. Critics of this analysis (such as Milton Friedman and Edmund Phelps) argued that the Phillips curve could not be a fundamental characteristic of economic general equilibrium because it showed a correlation between a real economic variable (the unemployment rate) and a nominal economic variable (the inflation rate). Their counter-analysis was that government macroeconomic policy (primarily monetary policy) was being driven by a low unemployment target and that this caused expectations of inflation to change, so that steadily accelerating inflation rather than reduced unemployment was the result. The resulting prescription was that government economic policy (or at least monetary policy) should not be influenced by any level of unemployment below a critical level - the "natural rate" or NAIRU.
The natural rate hypothesis and the NAIRU 
The idea behind the natural rate hypothesis put forward by Friedman was that any given labor market structure must involve a certain amount of unemployment, including frictional unemployment associated with individuals changing jobs and possibly classical unemployment arising from real wages being held above the market-clearing level by minimum wage laws, trade unions or other labour market institutions. Unexpected inflation might allow unemployment to fall below the natural rate by temporarily depressing real wages, but this effect would dissipate once expectations about inflation were corrected. Only with continuously accelerating inflation could rates of unemployment below the natural rate be maintained.
The analysis supporting the natural rate hypothesis was controversial, and empirical evidence suggested that the natural rate varied over time in ways that could not easily be explained by changes in labor market structures. As a result the "natural rate" terminology was largely supplanted by that of the NAIRU, which referred to a rate of unemployment below which inflation would accelerate, but did not imply a commitment to any particular theoretical explanation, or a prediction that the rate would be stable over time.
If is the NAIRU and is the actual unemployment rate, the theory says that:
- if for a few years, inflationary expectations rise, so that the inflation rate tends to accelerate;
- if for a few years, inflationary expectations fall, so that the inflation rate tends to slow (there is disinflation); and
- if , the inflation rate tends to stay the same, unless there is an exogenous shock.
Okun's law can be stated as saying that for every one percentage point by which the actual unemployment rate exceeds the so-called "natural" rate of unemployment, real gross domestic product is reduced by 2% to 3%.
The NAIRU analysis assumes that if inflation increases, workers and employers can create contracts that take into account expectations of higher inflation and agree on a level of wage inflation that matches the expected level of price inflation to maintain constant real wages. Therefore, the analysis requires inflation to accelerate to maintain low unemployment. However, this argument implicitly assumes that workers and employers cannot contract to incorporate accelerating inflation into wage expectations, but there is no clear justification for assuming that expectations or contract structures are limited in this way aside from the fact that such wage arrangements are not commonly observed.
The NAIRU analysis is especially problematic if the Phillips curve displays hysteresis, that is, if episodes of high unemployment raise the NAIRU. This could happen, for example, if unemployed workers lose skills so that employers prefer to bid up of the wages of existing workers when demand increases, rather than hiring the unemployed.
Others, such as Abba Lerner (1951, 1967) and Hyman Minsky (1965) have argued that a similar effect can be achieved without the human costs of unemployment via a job guarantee, where rather than being unemployed, those who cannot find work in the private sector should be employed by the government. This theory replaces the NAIRU with the NAIBER (non-accelerating-inflation-buffer employment ratio).
Relationship to other economic theories 
Most economists do not see the NAIRU theory as explaining all inflation. Instead, it is possible to move along a short run Phillips Curve (even though the NAIRU theory says that this curve shifts in the longer run) so that unemployment can rise or fall due to changes in inflation. Exogenous supply-shock inflation is also possible, as with the "energy crises" of the 1970s or the credit crunch of the early 21st century.
The NAIRU theory was mainly intended as an argument against active Keynesian demand management and in favor of free markets (at least on the macroeconomic level). There is, for instance, no theoretical basis for predicting the NAIRU. Monetarists instead support the generalized assertion that the correct approach to unemployment is through microeconomic measures (to lower the NAIRU whatever its exact level), rather than macroeconomic activity based on an estimate of the NAIRU in relation to the actual level of unemployment. Monetary policy, they maintain, should aim instead at stabilizing the inflation rate.
See also 
- Abba Lerner
- Edmund Phelps
- Job guarantee
- Milton Friedman
- Phillips curve
- Okun's Law
- Natural rate of unemployment
- Friedman, Milton. 1968. "The Role of Monetary Policy." American Economic Review 58 (March): 1 – 17.
- Coe, David T, Nominal Wages. The NAIRU and Wage Flexibility., Organisation for Economic Co-operation and Development
- Modigliani, Franco, and Lucas Papademos, 1975. “Targets for Monetary Policy in the Coming Year” Brookings Papers on Economic Activity, 141 – 165. The Brookings Institution.
- Robert M. Solow, Modigliani and Monetarism, p. 6.
- Hoover, Kevin D, "Phillips Curve", The Concise Encyclopedia of Economics (The Library of Economics and Liberty), retrieved 16 July 2007
- Ball, Laurence (2009), Hysteresis in Unemployment: Old and New Evidence
- William Mitchell, J. Muysken (2008), Full employment abandoned: shifting sands and policy failures, Edward Elgar Publishing, ISBN 1-85898-507-2
- Lerner, Abba P. (1951), The Economics of Employment
Further reading 
- Turner, Dave; et al (2001), "Estimating the Structural rate of Unemployment for the OECD Countries", OECD Economic Studies (Organisation for Economic Co-operation and Development) (33): 171–216, retrieved 16 July 2007
- Peter Bias, A Note on the Textbook Phillips Curve
- Prueba de Causalidad y Determinación de la NAIRU, Dr. J F Bellod Redondo