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Northwest Florida Map » |
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Population estimates methodology
The current population of the United States is obtained from the monthly Census population estimate. This is a very accurate and current estimate of the population and serves as the basis for projection and estimation at lower levels of geographic detail. The five and ten year projections have been derived from the middle-series projections of the Census Bureau.
The estimates rely heavily on the 2000 Census block level population counts, as these provide the most accurate recent data available. These 2000 Census counts replace the 1990 Census counts as the basis for undertaking estimates. In effect, the latest Census tabulation provides a baseline for the estimates and projections.
State and county level estimates are based on the compilation of data from a range of Federal and State authorities, including the latest county population estimates from the Census Bureau, reviews of building permit statistics, the current population survey (CPS), and additional local sources. Where required, the resulting estimates are then ratio-adjusted so that the sum of the county estimates is equal to the state total, and the state estimates equal to the national total. For the five- and ten-year projections, a similar method is employed. However, rather than using simple straight-line techniques, AGS uses straight-line methods only for growing areas. For declining areas, a log-normal extrapolation is used. This has the effect of slowing decline over time, which is characteristic of long-term population decline at the state level.
At the block group level, the population model consists of the application of a non-linear trend model which estimates population given historical patterns, INSOURCE population counts, and the latest Census age distributions (using cohort-survival techniques). Special consideration is given to the population age 65+ by applying ZIP code level counts by age and sex of all Medicare eligible persons.
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