United States Unemployment Rate

The labour force is defined as the number of people employed plus the number unemployed but seeking work. The participation rate is the number of people in the labour force divided by the size of the adult civilian noninstitutional population (or by the population of working age that is not institutionalised). The nonlabour force includes those who are not looking for work, those who are institutionalised such as in prisons or psychiatric wards, stay-at home spouses, kids, and those serving in the military. The unemployment level is defined as the labour force minus the number of people currently employed. The unemployment rate is defined as the level of unemployment divided by the labour force. The employment rate is defined as the number of people currently employed divided by the adult population (or by the population of working age). In these statistics, self-employed people are counted as employed.

Variables like employment level, unemployment level, labour force, and unfilled vacancies are called stock variables because they measure a quantity at a point in time. They can be contrasted with flow variables which measure a quantity over a duration of time. Changes in the labour force are due to flow variables such as natural population growth, net immigration, new entrants, and retirements from the labour force. Changes in unemployment depend on: inflows made up of non-employed people starting to look for jobs and of employed people who lose their jobs and look for new ones; and outflows of people who find new employment and of people who stop looking for employment.

When looking at the overall macroeconomy, several types of unemployment have been identified, including:
Frictional unemployment — This reflects the fact that it takes time for people to find and settle into new jobs. If 12 individuals each take one month before they start a new job, the aggregate unemployment statistics will record this as a single unemployed worker. Technological change often reduces frictional unemployment, for example: the internet made job searches cheaper and more comprehensive.
Structural unemployment — This reflects a mismatch between the skills and other attributes of the labour force and those demanded by employers. If 4 workers each take six months off to re-train before they start a new job, the aggregate unemployment statistics will record this as two unemployed workers. Technological change often increases structural unemployment, for example: technological change might require workers to re-train.
Natural rate of unemployment — This is the summation of frictional and structural unemployment. It is the lowest rate of unemployment that a stable economy can expect to achieve, seeing as some frictional and structural unemployment is inevitable. Economists do not agree on the natural rate, with estimates ranging from 1% to 5%, or on its meaning — some associate it with "non-accelerating inflation". The estimated rate varies from country to country and from time to time.
Demand deficient unemployment — In Keynesian economics, any level of unemployment beyond the natural rate is most likely due to insufficient demand in the overall economy. During a recession, aggregate expenditure is deficient causing the underutilization of inputs (including labour). Aggregate expenditure (AE) can be increased, according to Keynes, by increasing consumption spending (C), increasing investment spending (I), increasing government spending (G), or increasing the net of exports minus imports (X?M). {AE = C + I + G + (X?M)} (source: wikipedia)