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. COLORADO POPULATION ESTIMATES AND PROJECTIONS, 1980 - 2015 (June, 1991) o The following statement is a brief introduction to the attached population estimates and projections prepared by the Demographic Section of the Colorado Division of Local Government. These data represent part of a continuing effort by the Section to develop reasonable and accurate state and county population estimates and projections by significant groupings such as age, sex, ethnicity, and labor force status. (.' ) (;"") N (0 C,Q OVERVIEW AND RECENT CHANGES State and county population projections have been produced by a new system which models the relationship between demographic and economic change at the county level. The procedures can be summarized as follows: An initial population is projected by a cohort-component model. Projected labor force participation rates are then used to project the supply of labor produced by this population. This labor supply is compared with the demand for labor projected by an econometric model. Migration amounts are then adjusted so that the supply of labor is equal to the demand for labor for each year. This approach represents a refinement of the Division's previous projection system. Previously, future annual migration was set at the 25-year historical average for each county or region. With the new approach, annual migration varies depending on projections of labor supply and demand. No changes have been made in the cohort-component model which projects labor supply. Projections are normally based on the most recent July 1 population estimates produced by a multivariate estimation model in collaboration with the Census Bureau. These projections are based on July 1, 1990 projections which are extrapolations from April 1, 1990 census results using 1989-90 growth rates. Recently released evaluations of the 1990 census indicate a state-wide under count of approximately 82,000 or 2.4%. The Secretary of Commerce will decide by July 15, 1991 whether the Census Bureau will issue adjusted counts. These projections will be revised once that decision has been made. County estimates for 1981 - 1989 were prepared using a multivariate statistical model. The estimates have been revised to be consistent with 1990 census counts. The age-sex ,breakdown for both the estimates and projections was derived using a cohort-component model. As its name implies, a cohort-component model projects each component of population change separately (deaths, births, and net migration) while maintaining the cohort (age-sex) detail of population. In the first step of the basic operation of the model for each year, the number of people in each group is "survived" -- deaths are subtracted -- to the next year and the next age group. For example, 0 year olds in year 1 become 1 year olds in year 2, 1 year olds become 2, etc.. Fertility rates are then applied to the women of child-bearing age (15 - 49) to produce a new birth cohort for the year. Finally, migrants are added or subtracted from each age-sex group to achieve the estimated population or, for the projections, the population necessary to supply the labor force demanded by the economic forecast. The economic forecast was prepared in several stages by the Center for Business and Economic Forecasting (CBEF) affiliated with Regis College. In the first stage a State forecast of employment was prepared using their econometric model. The state employment numbers of this forecast were then distributed to BEA (U.S. Bureau of Economic Analysis) regions of the basis of BEA's 1990 forecast for the period. These resulting regional forecasts were then distributed to counties on the basis of the county's capture rations over the 1978 to 1988 period. (A county I s capture ratio is its proportion of the regional change that was received or "captured" by the county.) Finally, the civilian labor force of each county was forecast on the basis of the past relationship between labor force and ,-