OFFICIAL STATE ESTIMATES
Contents
This report presents preliminary state and county population estimates for July 1, 2010, July 1, 2011, July 1, 2012, July 1, 2013, July 1, 2014, July 1, 2015, July 1, 2016, July
1, 2017, July 1, 2018, and July 1, 2019, and components of population change.
Methodology
The state and county population are independently estimated using population change models benchmarked on official decennial census counts. The state population is estimated using the Driver License Address Change method. County population proportions are estimated using the average of three separately estimated sets of proportions. The final distribution of proportions is applied to the independently estimated state control.
State Estimate. The state population is estimated using the Driver License Address Change (DLAC) Method. This composite method separately estimates the population under age 18, 18 through 64, and 65 years and older. Administrative records such as births, deaths, driver license address changes, tax return data, Medicare and Medi-Cal enrollment, immigration reports, elementary school enrollments, and group quarters population are among the data used in this method. All data used to develop these estimates are in summary tables and do not reveal the identity of any individual.
County Estimates. Most of county populations estimates result from averaging the first three methods below. We use a Vital Statistics Method in nine counties with 65,000 populations or less.
DLAC Method. A modified version of the state Driver License Address Change (DLAC) method is used for counties. County proportions of the state total result from changes in county population values for births, deaths, school enrollment, foreign and domestic migration, medical care and medical aid enrollments, and group quarters population.
Ratio-Correlation Method. This method models change in household population as a function of changes in the distributions of driver licenses, school enrollments, and housing units. Estimates of county group quarters are added.
Tax Return Method. County proportions are derived by the U.S. Census Bureau using matched federal income tax returns to estimate inter-county migration along with vital statistics, group quarters, and other information for the population aged 65 and over.
Vital Statistics Method. County population estimates result from changes in county population values for births, deaths, and group quarters population.
This data series uses Census 2010 as a benchmark population. The Department of Finance estimates population each year based on population changes in births, deaths, domestic migration, and international migration. Following the release of the 2020 Decennial Census PL 94-171 redistricting data in August 2021, the department closed a gap between the 2010- 2020 estimates series and the 2020 Census data using intercensal population estimates method from Das Gupta in the 1980s. Postcensal data years of July 2020 and July 2021 also used the 2010 estimates base due to the lack of detailed age data in the current census release.
This estimate reflects revisions to the preliminary July 1, 2020 state and county estimates released in December 2020. The preliminary estimate had the state population at 39,761,200 and this year’s revised estimate for 2020 is 39,541,800, a downward revision of 219,400. The change mostly reflects the process of controlling to Census 2020 data.
Similar to the Census Bureau population estimates program, we use Das Gupta’s method for the 2010 to 2020 intercensal estimates. This method assumes that the population change from Census 2010 to 2020 is a geometric progression. Therefore, the differences between our current estimates and the Census 2020 can be distributed equally across each year during the decade. Nine counties (Alpine, Amador, Butte, Lake, Lassen, Plumas, Modoc, Trinity, and Tuolumne) in which the difference between the department’s estimates series and the 2020 Census was at least five percent are controlled by a non-linear model in order to better address year-specific large population changes in those counties.
Data Considerations
Sources. Data used in estimation models come from administrative records of numerous state and federal departments and agencies. Timeliness and coverage in these series vary. Corrections, adjustments or estimates may be made while preparing the estimates.
Accuracy. In general, estimates become less precise as the time from the last census increases. Data and models used to produce population estimates are subject to both measurement and non-measurement errors. This results in imperfect correlation between the data used to estimate the population and actual population change. The data and estimating models have been thoroughly tested with decennial census results that provide benchmarks for the estimates series. Data and methods are further refined and modified throughout the decade.
Acknowledgments
Phuong Nguyen produced the state and county estimates and prepared this report. Andres Gallardo produced the birth and death data. Douglas Kuczynski and John Boyne collected and prepared the group quarters data. Alex Alvarado produced the school enrollment projections. John Boyne validated input data, formulas, and methodologies used in the current state and county estimates series.
Suggested Citation
State of California, Department of Finance, E-6. Population Estimates and Components of Change by County, July 1, 2010-2019, Sacramento, California, December 2021