The U. S. Bureau of the Census prepares annual estimates by age and sex for the population of Puerto Rico at the commonwealth level. These estimates are based upon three components of population change: fertility (births), mortality (deaths), and migration (movement of people in and out of Puerto Rico).

All of the demographic data available for Puerto Rico are evaluated and, when appropriate, adjusted with the aid of an array of computer-based demographic analysis programs developed either by the U.S. Bureau of the Census or the United Nations. When we are satisfied that the data are of the highest possible quality, we produce the estimates using a computer program developed by the U.S. Census Bureau called the Rural Urban Projection Program (RUP). This program works with data at the level of single-year age groups to produce yearly estimates.

The estimates for Puerto Rico were made with the following data:

Base Population: We begin our estimates with data from the 1990 Census of Puerto Rico. An extensive evaluation of these data indicated that the children below the age of one were underrepresented in the official statistics. This problem was due in part to age misreporting and in part to simple omission. Therefore, in this exercise the size of this specific age group is adjusted before estimating the population.

Fertility: Registered births for the years 1990-1999 are used to estimate fertility.

Mortality: Registered deaths for the years 1990-1999 are used to estimate mortality.

International Migration: This component of population change is more difficult to estimate since there are no official registries of the movement of people into and out of Puerto Rico. In lieu of direct estimates, we derive an estimate of international migration based upon the pattern implied by comparing the censuses of 1980 and 1990.

Population estimates are available for the Commonwealth as a product of the Federal-State Cooperative Population Estimates Program, produced bu the U.S Census Bureau's Population Estimates Program.