The first step in projecting the county-level demographics forward is to project forward the race, ethnicity, and gender cohorts. Each cohort is trended forward using the published numbers of the past years. Initially, the numbers are projected forward using the sum of least squares, but the rate of change is damped slightly as the projected years get further beyond the base year.
The Census Bureau releases the County Population, Population Change and Estimated Components of Population Change files a number of months before releasing the full county level estimates. In the case when these files have been released but the full release has not, the first projection year is adjusted to match the total population published for each area.
Finally, the first four years of the projection are curve fit to avoid dramatic jumps from the base year to the first projection year.
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