Different countries keep track of demographics in different ways. The USA does a once every ten year census. Canada does a once every five year census. In Denmark, for example, the last census was done in 1981, because they keep a more real time tabulation of statistics through the use of public registers, rather than a point-in-time snapshot like the USA census. A number of European countries, Germany for example, have opted for real time tabulations rather than a census.