E-8 Historical Population and Housing Estimates for Cities, Counties and the State, 1990-2000

August 2007

Rationale for Preparing This Report

These revised intercensal estimates for 1990-2000 for the State, County, and City population and housing are produced by modifying previous estimates produced for the 1991-2000 decade to account for differences between the Finance test estimate on 4/1/2000 and enumerated census counts of the same day. The procedure to close these differences is called the "Error of Closure” (EOC). The concept is to preserve the original growth patterns that transpire in the annual DRU estimates for population and housing but to realign the ten year growth patterns with the bookend census data.

The EOC adjustment is applied after two consecutive censuses have been conducted; for this report, the two censuses are for 1990 and 2000. The EOC adjustment revises previously calculated intercensal estimates to mitigate the effects of estimation errors in a data series over the decade coupled with differential accuracy of two decennial censuses. For this report, the final adjustment was made after the 2000 census data became available. This procedure statistically distributes the difference, called the error, between the 2000 census counts and a "test" estimate calculated as of the census date - April 1, 2000 - to the previously calculated annual 1990 to 2000 estimates.

The E-8 report is similar to DRU's annually produced E-5 population and housing reports, except with reduced detail for housing units by type.  The aggregation of housing units into just the single-family, multi-family, and mobile home columns in the E-8 report, rather than the five categories displayed in the E-5 report, was necessary to guarantee continuity with differential censuses, including the changing nature of housing unit definitions between censuses, and to create increased accuracy given the self-reporting nature of the census process.  In addition, the EOC report also contains a date column.

Further discussion of the EOC technique and estimation procedures may be found in Appendix A.

 

Data Variables Description

The primary reports file E-8 Historical Population and Housing Estimates combine's data for all years by municipality and is arranged as follows:

  • Column one of this report alphabetically lists jurisdictions by county and city.
  • Column two displays the year for the provided data.

Population Items:  Data in columns three through five provide population counts.

  • Column three shows total population for the area.
  • Column four shows the number of persons living in occupied housing units (household population).
  • Column five displays the population living in group quarters (non-household population) such as nursing homes, school dormitories, state and federal prisons, and military barracks.

Group quarters population (column five) plus household population (column four) equals the total population for an area (column three).

Housing Items:  Columns six through eleven provide data on housing units broken down as follows:

  • Column six shows the total stock of housing units, including year-round, vacant seasonal or migratory units, and other vacant units. 
  • Columns seven through nine differentiate types of housing units. These columns combined will sum to Column 6.
  • Column 7: Single family dwelling units include single family detached units (units which are detached from any other structure and have open space on all four sides) and single family attached dwellings (units which are attached to other units with adjoining walls extending from ground to roof that separate them from other adjoining structures and forms a property line). Each single family unit has its own heating system.
  • Column 8:  Multiple family dwelling units include structures with 2 or more housing units. (Note: Almost 125,000 respondents to the 1990 Census listed their residence as "other", rather than any of the provided categories. For this report, "other" housing units have been allocated to the multiple family dwelling units category on the advice of the U.S. Census Bureau.)
  • Column 9:  Mobile homes include both occupied and vacant mobile homes used for residential housing.

Condominiums are considered an ownership classification, not a structural description, so they may be included in all types of units:

Other Data:

  • Column 10 displays total occupied housing units (households).
  • Column 11 displays the percent of vacant housing units, or Vacancy Rate, for the area. This is the difference between total and occupied housing units (column 6 minus column 10) divided by total housing units (column 6) and displayed as a percentage.
  • Column 12 represents the average number of persons per household (PPHH) which is derived by dividing household population by occupied housing units (column 4 divided by column 10)

Methodology

City Estimates.  The Housing Unit Method (HUM) estimates total and occupied housing units, household size, household population, and group quarters population. Housing units (HU) are estimated by adding new housing construction, units added by conversions, and annexed housing units, then subtracting units lost to demolitions or fires, units lost from conversions, and de-annexed units, from the 1990 baseline housing benchmark or a prior year’s estimate. The HU changes are supplied by local jurisdictions, the U.S. Census Bureau, and Military Installations. Occupied HUs is estimated by applying a derived civilian vacancy rate, based on census benchmark data, to the estimated civilian HUs. Adjustments to the census occupancy rates (occupied units/total units) are occasionally made to account for changing vacancy rates such as adding vacancies in areas with rapid housing growth.  Occupied military units are added to civilian occupied units to calculate total occupied HUs. Military surveys are used to track military changes, including base realignments and closures. The household population estimate is derived by multiplying the number of occupied HUs by the current persons per household. The persons per household estimates are based on 1990 benchmark data and are updated by incorporating the current county population series into these estimates. Persons per household can be further changed when a jurisdiction adds large numbers of special types of housing, such as adult living. The benchmark group quarters population is updated using the reported population change in group quarters facilities. The household and group quarters populations are summed to produce the initial city population estimates. These estimates are aligned to the county estimates described below.

Sub-county total population estimates have been controlled to the county EOC estimates, and the county EOC estimates were controlled to the state EOC estimates as well.  Group quarters population, all of the housing columns, and occupied housing units were created at the sub-county level, thus were aggregated to account for county and state totals.  This report contains calculated columns for household population, vacancy rate and persons per household.

County Estimates.  County population proportions result from averaging three methods:

  • 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 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, housing units, and deaths. Estimates of county group quarters are added.
  • The Tax Return Method. This method represents the proportions derived from the independent county populations produced by the U.S. Census Bureau.

Of the county methods used during the 1990’s, the Household Method was used in estimating county proportions of state population until January 1997.  This method was dropped in the following year. The Household Method estimates the annual proportionate change in each county's distribution of households compared to the prior year. The estimated change is applied to the prior estimated distribution of the household population. Group quarters estimates are then added.

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 are in summary tables and do not reveal the identity of any individual.

Data Considerations

Sources.  Data used in estimation models come from administrative records of several state and federal government departments and agencies, as well as numerous local jurisdictions. Since timeliness and coverage in these series vary, corrections, smoothing, and other adjustments may be applied.

Accuracy.  Data and models used to produce population estimates are subject to measurement and non-measurement errors. The data and estimating models were thoroughly tested with decennial census results that provide benchmarks for the estimates series. The total state estimate was within one-half of one percent (0.5%) of the 2000 census count; county estimates varied by an average of 1.9 percent, and city estimates by an average of 5.6 percent. .

Acknowledgments

Daniel Sheya prepared this report and the city estimates.  Linda Gage prepared the state and county estimates, Walter Schwarm and Doug Kuczynski provided analytical expertise in city estimates while producing military, group quarters, household population and housing estimates.  Mary Heim, Chief of the Demographic Research Unit (DRU), and John Malson, Research Manager over the city estimates section provided general direction.

Suggested Citation

State of California, Department of Finance, E-8 Historical Population and Housing Estimates for Cities, Counties, and the State, 1990-2000. Sacramento, California, August 2007.

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