The natural rate of unemployment (sometimes called the structural unemployment rate) is a concept of economic activity developed in particular by Milton Friedman and Edmund Phelps in the 1960s, both recipients of the Nobel prize in economics. In both cases, the development of the concept is cited as a main motivation behind the prize. It represents the hypothetical unemployment rate consistent with aggregate production being at the "long-run" level. This level is consistent with aggregate production in the absence of various temporary frictions such as incomplete price adjustment in labor and goods markets. The natural rate of unemployment therefore corresponds to the unemployment rate prevailing under a classical view of determination of activity. It is mainly determined by the economy's supply side, and hence production possibilities and economic institutions. If these institutional features involve permanent mismatches in the labor market or real wage rigidities, the natural rate of unemployment may feature involuntary unemployment.
Occurrence of disturbances (e.g., cyclical shifts in investment sentiments) will cause actual unemployment to continuously deviate from the natural rate, and be partly determined by aggregate demand factors as under a Keynesian view of output determination. The policy implication is that the natural rate of unemployment cannot permanently be reduced by demand management policies (including monetary policy), but that such policies can play a role in stabilizing variations in actual unemployment. Reductions in the natural rate of unemployment must, according to the concept, be achieved through structural policies directed towards an economy's supply side.
The natural rate hypothesis
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. Philip’s Curve
The Phillips curve represents the relationship between the rate of inflation and the unemployment rate. Although he had precursors, A. W. H. Phillips’s study of wage inflation and unemployment in the United Kingdom from 1861 to 1957 is a milestone in the development of macroeconomics. Phillips found a consistent inverse relationship: when unemployment was high, wages increased slowly; when unemployment was low, wages rose rapidly.
Phillips conjectured that the lower the unemployment rate, the tighter the labor market and, therefore, the faster firms must raise wages to attract scarce labor. At higher rates of unemployment, the pressure abated. Phillips’s “curve” represented the average relationship between unemployment and wage behavior over the business cycle. It showed the rate of wage inflation that would result if a particular level of unemployment persisted for some time.
Economists soon estimated Phillips curves for most...