methodology

2004 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. County population estimates are produced with a component of change population method, which updates the latest census population using data on births, deaths, internal and international migration. A more detailed description of the county methodology can be found here. 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 geographically updated each year to reflect legal changes reported in the Boundary and Annexation Survey (BAS), Census corrections and other administrative revisions.

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, 2004 estimates are used here as an example.

HU₀₄ = HU₀₀ + (NC₀₄ + NM₀₄) - HL₀₄

Where:

HU04	=	Estimated 2004 housing units
HU00	=	GUSSIE updated Census 2000 housing units
NC04	=	Estimated residential construction, April 1, 2000 to July 1, 2004
NM04	=	Estimated new residential mobile home placements, April 1, 2000 to July 1, 2004
HL04	=	Estimated residential housing loss, April 1, 2000 to July 1, 2004

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) --Census 2000 counts of housing units at the subcounty level reflect BAS updates that are legally effective as of January 1, 2004. The housing unit counts also include Count Question Resolution (CQR) actions, and administrative revisions benchmarked in the TIGER System and the Master Address File (MAF) through May of 2004.

1B. Estimated Residential Construction (NC₀₄) --New residential construction was calculated using the following formula:

NC₀₄ = (BP₀₄ * 0.98) + NPC₀₄

Where:

NC04	=	Estimate of new residential construction for the period: April 1, 2000 to July 1, 2004
BP04	=	The residential building permits that result in the construction of new units for the period April 1, 2000 to July 1, 2004 include permits issued in calendar years 2000-2003 (accounting for a six-month lag time between permit issuance and completed construction).
NPC04	=	Estimate of new residential construction in non-permit issuing areas for the period: April 1, 2000 to July 1, 2004

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 (NM₀₄) -- 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 2004 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 (HL₀₄) -- The method for estimating housing unit loss has been revised for the 2004 estimates. The 2004 estimates of housing unit loss are based on data derived from the 1997-2003 American Housing Survey (AHS) national sample. The following three types of AHS noninterviews were considered to represent permanent loss of a housing unit.

Type B, 16 -- Interior exposed to the elements

Type C, 30 –- Demolished or disaster loss

Type C, 31 –- House or Mobile Home moved

Housing unit loss rates based on these non-interview types were then developed for housing units based on structure type and age of structure. The rates are as follows:

Mobile Homes: 1.58 percent
House, Apartment, or Flat built in:
1990-2000: 0.031 percent
1980-1990: 0.054 percent
1970-1980: 0.103 percent
1960-1970: 0.172 percent
1950-1960: 0.249 percent
1940-1950: 0.324 percent
1930-1940: 0.364 percent
Overall loss rate: 0.295 percent

Step 2. Producing an Uncontrolled Subcounty Household Population Estimate

The uncontrolled subcounty household population estimate is derived by:

UCHHP₀₄ = HU₀₄ * OCC₀₀ * PPH₀₀

Where:

UCHHP04	=	Uncontrolled subcounty household population estimate for 2004
HU04	=	July 1, 2004 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:

SCEST₀₄ = [UCHHP₀₄*(CHP₀₄/SUCHHP₀₄)] + GQ₀₄

Where:

SCEST04	=	Final 2004 subcounty population estimate
UCHHP04	=	Uncontrolled 2004 household population estimate
CHP04	=	Published county 2004 household population estimate
SUCHHP04	=	County sum of UCHHP04 for all subcounty areas
GQ04	=	2004 group quarters population estimate

Published County Estimate (CHP₀₄) --The published county population estimate as calculated by the Administrative Records Method for the current estimate year.

County Sum of Uncontrolled Household Population Estimates (SUCHHP₀₄) --The county sum of the uncontrolled county population is obtained by summing the estimates for all subcounty areas within a county.

Group Quarters (GQ₀₄) -- 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 prepare 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.