That can impact non-industrialized economies, such as the United States and Europe in the early 19th century, since overall unemployment was approximately 3% because so many individuals were self-employed, independent farmers; however, non-agricultural unemployment was as high as 80%.Many economies industrialize and so experience increasing numbers of non-agricultural workers. For example, the United States non-agricultural labour force increased from 20% in 1800 to 50% in 1850 and  97% in 2000. The shift away from self-employment increases the percentage of the population that is included in unemployment rates. When unemployment rates between countries or time periods are compared, it is best to consider differences in their levels of industrialization and self-employment. Additionally, the measures of employment and unemployment may be "too high." In some countries, the availability of unemployment benefits can inflate statistics by giving an incentive to register as unemployed. People who do not seek work may choose to declare themselves unemployed to get benefits; people with undeclared paid occupations may try to get unemployment benefits in addition to the money that they earn from their work.However, in the United States, Canada, Mexico, Australia, Japan, and the European Union, unemployment is measured using a sample survey (akin to a Gallup poll). According to the BLS, a number of Eastern European nations have instituted labour force surveys as well. The sample survey has its own problems because the total number of workers in the economy is calculated based on a sample, rather than a census.
Since not all unemployment may be "open" and counted by government agencies, official statistics on unemployment may not be accurate. In the United States, for example, the unemployment rate does not take into consideration those individuals who are not actively looking for employment, such as those who are still attending college.According to the OECD, Eurostat, and the US Bureau of Labor Statistics the unemployment rate is the number of unemployed people as a percentage of the labour force. "An unemployed person is defined by Eurostat, according to the guidelines of the International Labour Organization, as:

someone aged 15 to 74 (in Italy, Spain, the United Kingdom, Iceland, Norway: 16 to 74 years);
without work during the reference week;
available to start work within the next two weeks (or has already found a job to start within the next three months);
actively having sought employment at some time during the last four weeks. "The labour force, or workforce, includes both employed (employees and self-employed) and unemployed people but not the economically inactive, such as pre-school children, school children, students and pensioners.The unemployment rate of an individual country is usually calculated and reported on a monthly, quarterly, and yearly basis by the National Agency of Statistics. Organisations like the OECD report statistics for all of its member states.Certain countries provide unemployment compensation for a certain period of time for unemployed citizens who are registered as unemployed at the government employment agency.