Methodology

2003 ESTIMATES AND PROJECTIONS AREA DOCUMENTATION
SUBCOUNTY TOTAL POPULATION ESTIMATES

PDF Version of this Methodology

BACKGROUND

The U.S. Census Bureau produces estimates of total resident population for all areas of general-purpose government on an annual basis. The subcounty areas consist of both incorporated places, such as cities, boroughs, and villages, and minor civil divisions such as towns and townships. We produce subcounty population estimates by a housing unit method that uses housing unit change to distribute county population to subcounty areas. In addition to their use in producing subcounty population estimates, housing unit estimates at the subcounty level are aggregated to the county and state levels and released as a separate data product.

SUBCOUNTY POPULATION ESTIMATES METHODOLOGY

The Census Bureau develops subcounty population estimates using the "Distributive Housing Unit Method" which uses housing unit estimates to distribute the county population to subcounty areas within the county. Housing unit estimates use building permits, mobile home shipments, and estimates of housing unit loss to update housing unit change since the last census. Census counts of housing units are updated each year through the Geographic Update System to Support Intercensal Estimates (GUSSIE).

We develop a household population estimate by applying the occupancy rate and average persons per household (PPH) from the latest census to an estimate of housing units. The estimate obtained from this method is then controlled to the final county population estimate. The non-household population is measured by the change in the group quarters population. We produce the final estimate by adding the population in group quarters to the household population. The assumption implicit in this method is that changes in the occupancy rate and/or the PPH are measured by the updated county population estimate and that the rate of change in the occupancy rate and/or PPH is uniform within counties.

The estimates are produced using the following steps:

Step 1. Estimating Housing Units

We produce housing unit estimates for each area by the component model described below. The July 1, 2003 estimates are used here as an example.

HU03 = HU00 + (NC03 + NM03) - HL03

Where:

HU03 = Estimated 2003 housing units
HU00 = GUSSIE updated Census 2000 housing units
NC03 = Estimated residential construction, April 1, 2000 to July 1, 2003
NM03 = Estimated new residential mobile home placements, April 1, 2000 to July 1, 2003
HL03 = Estimated residential housing loss, April 1, 2000 to July 1, 2003

Note: For the 3 month period from April 1, 2000 to July 1, 2000, a factor of 0.25 is applied to the year 2000 input data.

1A. Census 2000 Housing Units (HU00) --Through GUSSIE, Census 2000 counts of housing units at the subcounty level are updated each year to reflect boundary updates, Count Question Resolution (CQR) actions, and administrative revisions. The boundary updates reflect three cycles of the Boundary and Annexation Survey (BAS) and represent boundaries that are legally effective as of January 1, 2003. The CQR actions and administrative revisions include those benchmarked in the TIGER System and the Master Address File (MAF) through May of 2003.

1B. Estimated Residential Construction (NC03) --New residential construction was calculated using the following formula:

NC03 = (BP03 * 0.98) + NPC03

Where:

NC03 = Estimate of new residential construction for the period: April 1, 2000 to July 1, 2003
BP03 = The residential building permits that result in the construction of new units for the period April 1, 2000 to July 1, 2003 include permits issued in calendar years 2000, 2001 and 2002 (accounting for a six-month lag time between permit issuance and completed construction).
NPC03 = Estimate of new residential construction in non-permit issuing areas for the period: April 1, 2000 to July 1, 2003

Note: For the 3 month period from April 1, 2000 to July 1, 2000, a factor of 0.25 is applied to the year 2000 input data.

Building permit data are compiled from internal data files developed by Manufacturing and Construction Division (MCD). These files include imputed permits where a jurisdiction did not report permit issuance for the entire year. Housing growth calculated from building permits employs a six-month lag time between the issuance of permits and completion of construction.

Two percent of all building permits never result in the actual construction of a housing unit (as derived from U.S. Census Bureau Current Construction Reports, Series C-20 and Series C-22). Therefore, a factor of 0.98 is used to estimate completed new units.

The annual Survey of Construction (SOC) produces regional estimates of housing units constructed in non-permit issuing jurisdictions. The regional SOC estimates are then distributed to all subcounty areas that have no record of issuing permits for the estimates period. This distribution is based on the subcounty area’s share of the regional total of units in nonpermit-issuing jurisdictions as of Census 2000.

1C. Estimated New Mobile Home Placements (NM03) --The Census Bureau does not collect updated data at the subcounty level on mobile home placements. We derive estimates for mobile homes by allocating state mobile home shipment data to subcounty areas based on the subcounty area’s share of state mobile homes in Census 2000.

We receive monthly reports on mobile home shipments from MCD. These monthly reports are then summed to calculate the annual total of state mobile home shipments.

To allocate the state mobile home shipment data to subcounty areas, we apply the subcounty area’s share of state mobile homes as of Census 2000 to the updated number of mobile home shipments. Because type of structure (the item indicating that a housing unit is a mobile home) was not a 100 percent item in Census 2000, sample data were used to produce the 2003 estimates of mobile homes at the subcounty level. The following steps describe the process of producing sample data that were consistent with the 100 percent housing unit data in current estimates geography.

  1. Match each unit in the Sample Edited Detail File (SEDF) to the geographically updated 100% Detail File (HDF) extract, by unit identification number.
  2. Apply the updated geographic codes from the HDF (higher level, census tract, and block) to the SEDF records.
  3. Re-tabulate the sample data with the sample weights for the primitive geographic areas into which they now are aggregated after the geographic update.
  4. Multiply the sample data tallies in each primitive geographic area by the ratio of housing units in the tabulation Census 2000 HDF to the housing units in the tabulation Census 2000 SEDF.
  5. Aggregate the results to all estimates universe summary levels.

1D. Estimated Housing Loss (HL03) --The 2003 estimates of housing unit loss are based on data derived from the 1993 Components of Inventory Change Survey (CINCH) and 1990 Census data. The CINCH survey identified the following four types of housing units to be at a greater risk of loss:

  1. Mobile homes
  2. Older units (constructed before 1939)
  3. Vacant for Seasonal or Recreational Use
  4. Boarded up
Step 2. Producing an Uncontrolled Subcounty Household Population Estimate

The uncontrolled subcounty household population estimate is derived by:

UCHHP03 = HU03 * OCC00 * PPH00

Where:

UCHHP03 = Uncontrolled subcounty household population estimate for 2003
HU03 = July 1, 2003 housing unit estimate
OCC00 = Census 2000 occupancy rate
PPH00 = Census 2000 persons per household
Step 3. Producing a Final Subcounty Population Estimate

The final step in producing a population estimate using the Distributive Housing Unit Method is controlling the uncontrolled subcounty estimates to the published county totals. The following equation describes the calculation of a controlled estimate:

SCEST03 = [UCHHP03*(CHP03/SUCHHP03)] + GQ03

Where:

SCEST03 = Final 2003 subcounty population estimate
UCHHP03 = Uncontrolled 2003 household population estimate
CHP03 = Published county 2003 household population estimate
SUCHHP03 = County sum of UCHHP03 for all subcounty areas
GQ03 = 2003 group quarters population estimate

Published County Estimate (CHP03) --The published county population estimate as calculated by the Administrative Records Method for the current estimate year.

County Sum of Uncontrolled Household Population Estimates (SUCHHP03) --The county sum of the uncontrolled county population is obtained by summing the estimates for all subcounty areas within a county.

Group Quarters (GQ03) --This component is primarily a combination of military personnel living in barracks, college students living in dormitories and persons residing in institutions. Inmates of correctional facilities and persons in health care facilities and Job Corp centers are also included in this category.

We use group-quarters population data from two sources to estimate subcounty populations: (1) Census 2000 counts of group-quarters population by facility type for each subcounty area, and (2) a time series of individual group-quarters records from the Group Quarters Report (GQR). State representatives of the Federal State Cooperative Program for Population Estimates complete the GQR.

These two sets of group-quarters population data are used to derive a time series of group-quarters population through the following process:

Part 1. We sum the group-quarters populations from Census 2000 and the GQR to the subcounty level by the seven facility types for each estimate date in the time series.

Part 2. The time series of subcounty group-quarters population by GQ type is then calculated by adding the year-to-year change given by the GQR data to the Census 2000 count of the GQ population.