Thus governments, businesses, and anyone interested in analyzing economic performance must have accurate population estimates. Population estimates are usually based on national censuses, but the frequency and quality of these censuses vary by country.
Most countries conduct a complete enumeration no more than once a decade.
Precensus and postcensus estimates are interpolations or extrapolations based on demographic models. Moreover, the international comparability of population indicators is limited by differences in the concepts, definitions, data collection procedures, and estimation methods used by national statistical agencies and other organizations that collect population data. The currentness of a census, along with the availability of complementary data from surveys or registration systems, is one of many objective ways to judge the quality of demographic data. In some European countries registration systems offer complete information on population in the absence of a census. See Primary data documentation for the most recent census or survey year and for registration completeness.