employment" In demands based theory, it is possible to abolish cyclical unemployment by increasing the aggregate demand for products and workers. However, the economy eventually hits an "inflation barrier" that is imposed by the four other kinds of unemployment to the extent that they exist. Historical experience suggests that low unemployment affects inflation in the short term but not the long term. In the long term, the velocity of money supply measures such as the MZM ("money zero maturity", representing cash and equivalent demand deposits) velocity is far more predictive of inflation than low unemployment. Some demand theory economists see the inflation barrier as corresponding to the natural rate of unemployment. The "natural" rate of unemployment is defined as the rate of unemployment that exists when the labour market is in equilibrium, and there is pressure for neither rising inflation rates nor falling inflation rates. An alternative technical term for that rate is the NAIRU, the Non-Accelerating Inflation Rate of Unemployment. Whatever its name, demand theory holds that if the unemployment rate gets "too low," inflation will accelerate in the absence of wage and price controls (incomes policies). One of the major problems with the NAIRU theory is that no one knows exactly what the NAIRU is, and it clearly changes over time. The margin of error can be quite high relative to the actual unemployment rate, making it hard to use the NAIRU in policy-making. Another, normative, definition of full employment might be called the ideal unemployment rate. It would exclude all types of unemployment that represent forms of inefficiency. This type of "full employment" unemployment would correspond to only frictional unemployment (excluding that part encouraging the McJobs management strategy) and so would be very low. However, it would be impossible to attain this full-employment target using only demand-side Keynesian stimulus without getting below the NAIRU and causing accelerating inflation (absent incomes policies). Training programs aimed at fighting structural unemployment would help here. To the extent that hidden unemployment exists, it implies that official unemployment statistics provide a poor guide to what unemployment rate coincides with "full employment." Structural unemployment Structural unemployment occurs when a labour market is unable to provide jobs for everyone who wants one because there is a mismatch between the skills of the unemployed workers and the skills needed for the available jobs. Structural unemployment is hard to separate empirically from frictional unemployment except that