Demographic indicators are internationally recognized and commonly used key figures for describing population structure and population movement. Formal demography, which relates population levels and movements deterministically, provides a generally accepted mathematical basis for calculating demographic indicators. These include measures of population structure, fertility and mortality, marriage and divorce patterns, and migration and naturalization. These commonly used indicators include the total fertility rate, life expectancy, first marriage rate and total divorce rate, migration and naturalization rates, and measures of population structure such as the proportion of the 65+ generation. A special form of indicators are the demographic tables, the best known of which are the mortality tables.