Our data for the population model come from the United Nations Population Division revisions of data and forecasts, released every second year. We take population by age and sex from that source, as well as historical series for life expectancy, total fertility rate, and infant mortality. We also pull in their migration data.
Often they present their data values in 5 year categories (1950-1955, . . . , 2095-2099). To obtain values at specific 5-year intervals, such as 1960 or 2010, we average the values for the two 5-year categories that bracket that year. To estimate annual values for all years from such categories, for instance for migration numbers, we used a Sprague algorithm to spread the 5 year data (1950-1955, . . . , 2095-2099). With respect to migration, to obtain net migration rates we divided their annualized numbers by annual population data.