State Household and Housing Unit Estimation Methodology: 1990-1998 Source: U.S. Census Bureau Internet Release date: December 8, 1999 Housing Unit Estimates Housing unit estimates for each state were developed by the component model described below. The July 1, 1998 estimates are used here as an example. 1. HU98 = HU90 + (NC98 + NM98) - HL98 Where: HU98 = Estimated 1998 housing units HU90 = 1990 census housing units NC98 = Estimated residential construction, April 1, 1990 to July 1, 1998 NM98 = Estimated new residential mobile home placements, April 1, 1990 to July 1, 1998 HL98 = Estimated residential housing loss, April 1, 1990 to July 1, 1998 Explanations of each component follow: Estimated residential construction for the period April 1, 1990 to July 1, 1998. Building permits were compiled from internal data files (1989 - 1998) developed by Manufacturing and Construction Division. 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 census region-specific lag time (weighted average by number of units in structure) between the issuance of permits and completion of construction. The lag times by census region (in number of months) are: U.S. average 7.5 Northeast Region 8.3 Midwest Region 7.5 South Region 7.2 West Region 8.7 Two percent of all building permits never result in the actual construction of a housing unit (as derived from U.S. Bureau of the Census Current Construction Reports, Series C20-9103 and Series C22-9107). Therefore, a factor of .98 is used to estimate completed new units. New residential construction was calculated in the following manner for the July 1, 1998 estimates: 2. NC98 = [[(BP89 + BP90 + BP91 +... BP97] * .98] + NPC98 Where: NC98 = Estimate of new residential construction for the period: April 1, 1990 to July 1, 1998 BP89 = Residential building permits issued in 1989 that would result in the completion of a housing unit after April 1, 1990 and prior to the date of the estimate. BP90 = Residential building permits issued in 1990 that would result in the completion of a housing unit after April 1, 1990 and prior to the date of the estimate. BP91 = Residential building permits issued in 1991 that would result in the completion of a housing unit prior to the date of the estimate. BP97 = Residential building permits issued in 1997 that would result in the completion of a housing unit prior to the date of the estimate. NPC98 = Estimate of new residential construction in non- permit issuing areas for the period: April 1, 1990 to July 1, 1998 Note: NPC98 was developed by a procedure which creates estimates of residential construction where building permits are not issued. The Survey of Construction provides annual national estimates of units constructed without building permits. The 1998 estimate of state non-permit construction is calculated by applying the 1990 state proportion of units in nonpermit issuing jurisdictions to the updated national total of nonpermit construction. Estimated new residential mobile home placements for the period April 1, 1990 to July 1, 1998. Tabulations of mobile homes shipped to states are consistent with Series C-40 reports (U.S. Bureau of the Census, 1998). Ninety-eight percent of all mobile homes shipped to states are used for residential purposes. Internal studies have shown that on average a two month lag time exists between the time when a mobile home is shipped and subsequently put in place for residential use (Schwanz, 1986). These factors result in the development of the following formula. 3. NM98 = [(MH90*(11/12)) + MH91 + MH92 + ... (MH98*(4/12))] * .98 Where: NM98 = Estimated new residential mobile home placements since April 1, 1990 MH90 = Mobile homes shipped to states in 1990 MH91 = Mobile homes shipped to states in 1991 MH92 = Mobile homes shipped to states in 1992 MH98 = Mobile homes shipped to states in 1998 Estimated residential housing loss for the period April 1, 1990 to July 1, 1998. Demolition permits were compiled from internal data files (1990-1995) developed by Manufacturing and Construction Division. These files include imputed permits where a permit issuing jurisdiction did not report permit issuance for the entire year. No lag time is assumed for demolition permits. 4. HL98 = (.75 * DP90) + DP91 + DP92 + ... (.5 * DP95) + DL98 Where: HL98 = Estimate of housing loss for the period: April 1, 1990 to July 1, 1998 DP90 = Residential demolition permits issued in 1990 DP91 = Residential demolition permits issued in 1991 DP92 = Residential demolition permits issued in 1992 DP95 = Residential demolition permits issued in 1995 DL98 = Estimated housing unit loss not measured by demolition permits for the period, April 1, 1990 to July 1, 1998 Note: The Census Bureau stopped collecting demolition permit data after 1995. After 1995, all data on housing unit loss is estimated. Estimated housing unit loss where no permit was issued was developed by a procedure which creates estimates of housing unit loss for substate areas. These estimates were then aggregated to state totals. National estimates from the Components of Inventory Change (CINCH) study show that permitted demolitions accounted for only 40% of the total housing unit loss. CINCH data show that certain types of units exhibit a greater risk to loss. These types of units include: 1. Mobile homes and other 2. Older units (pre-1939 construction) 3. Vacant for seasonal and recreational use 4. Boarded up Regional totals of nonpermit housing unit loss are distributed to states based on the 1990 state share of the region's total of units at risk to loss. The 1990 proportion is then applied to an updated regional total of housing unit loss. Note: In essence, this process applies a crude death rate to the housing inventory to develop a baseline estimate of housing unit loss. This crude death rate is refined by the type of housing stock contained within each state. State Households and Age of Householder Estimates The household by age of householder estimates for each state were developed by the model described below. First, the model applies the change in national household formation rates by age of householder (as measured through CPS data) to the 1990 decennial census state specific household formation rates by age. This process produces estimates of state household formation rates by age. Next, the updated state household formation rates are applied to state population estimates by age to develop estimates of households by age of householder. The estimate of a state's total households is the summation of that state's households by age of householder. The following equation provides an example of how the July 1, 1998 estimates were developed: 1. HH98j = ((HHR98j/HHR90j) * CHHR90j) * PA98j Where: j = Age groups (15-24, 25-34, 35-44, 45-54, 55-64, 65-74 75+) HH98 = Estimate of households: July 1, 1998 HHR98 = U.S. householder rate from the March 1998 CPS HHR90 = U.S. householder rate from the March 1990 CPS CHHR90 = 1990 census householder rate PA98 = Total population estimate: July 1, 1998 DEFINITIONS AND EXPLANATIONS Housing Units. A housing unit is a house, an apartment, a mobile home, a group of rooms, or a single room that is occupied (or if vacant is intended for occupancy) as separate living quarters. Separate living quarters are those in which the occupants live and eat separately from any other persons in the building and which have direct access from the outside of the building or through a common hall. The occupants may be a single family, one person living alone, two or more families, or any other group of related or unrelated persons who share living arrangements. For vacant units, the criteria of separateness and direct access are applied to the intended occupants wherever possible. Both occupied and vacant housing units are included in the housing unit inventory, except that recreational vehicles, boats, vans, tents, railroad cars, and the like are included only if they are occupied as someone's usual place of residence. Vacant mobile homes are included provided they are intended for occupancy on the site where they stand. Vacant mobile homes on dealer's sales lots, at the factory, or in storage yards are excluded from the housing unit inventory. Group Quarters. Living quarters of the following types are classified as group quarters and are excluded from the housing unit inventory: Dormitories, bunkhouses, and barracks; quarters in predominantly transient hotels, motels, and the like, except those occupied by persons who consider the hotel their usual place of residence; quarters in institutions, general hospitals, and military installations except those occupied by staff members or resident employees who have separate living arrangements. Furthermore, if living quarters contain 9 or more persons unrelated to the householder or person in charge (a total of 10 unrelated persons), they are classified as group quarters. If the living quarters contain eight or fewer persons unrelated to the householder or person in charge, they are classified as housing units. Occupied Housing Units. A housing unit is classified as occupied if it is the usual place of residence of the person or group of persons living in it. By definition, the number of occupied housing units is equivalent to the number of households or householders. Vacant Housing Units. A housing unit is classified as vacant if no one is living in it, unless its occupants are only temporarily absent. New units not yet occupied are classified as vacant housing units if construction has reached a point to which all exterior windows and doors are installed and final usable floors are in place. Vacant units are excluded if they are open to the elements; that is, the roof, walls, windows, and/or doors no longer protect the interior from the elements, or if there is positive evidence that the unit is condemned or is to be demolished. Also excluded are quarters being used entirely for nonresidential purposes, such as a store or an office, or quarters used for the storage of business supplies or inventory, machinery, or agricultural products. Household. A household includes all the persons who occupy a housing unit. The occupants may be a single family, one person living alone, two or more families, or any other group of related or unrelated persons who share living arrangements, except where there are 9 or more persons unrelated to the householder (see Group Quarters, above). Persons Per Household. A measure obtained by dividing the number of persons in households by the number of households. Householder. The householder refers to the person (or one of the persons) in whose name the housing unit is owned or rented or, if there is no such person, any adult member, excluding roomers, boarders, or paid employees. If the house is jointly owned by a married couple, either the husband or wife may be listed first, thereby becoming the reference person, or householder, to whom the relationship of the other household members is recorded. One person in each household is designated as the householder. Mobile Homes. Mobile home statistics used in the housing unit estimation process are produced by the National Conference of States on Building Codes and Standards. In this series, a mobile home is defined as a moveable dwelling, eight feet or more wide and forty feet or more long, designed to be towed on its own chassis, with transportation gear integral to the unit when it leaves the factory, and without need of a permanent foundation. These mobile homes include multiwides, which are counted as single units. Excluded are travel trailers, motor homes, and modular housing. The shipment figures are based on reports submitted by manufacturers on the number of mobile homes actually shipped during the survey month. Shipments to dealers may not be placed for residential uses in the same month as they are shipped. The number of mobile homes used for residential purposes has been estimated at ninety-eight percent. Building and Demolition Permits. Statistics on building and demolition permits for privately-owned housing units are based upon reports submitted to the U.S. Bureau of the Census by 17,000 local building permit officials in response to mail surveys. When a report is not received, missing data are either (1) obtained from the Survey of Use of Permits (SUP) which is used to collect information on housing starts, or (2) imputed. Data from the SUP are available only for about 850 places for which the Census Bureau interviewers list and sample the permits that authorized construction of new residential structures. For places not in the SUP, imputations are used. Imputations for building permits are based on the assumption that the ratio of current month authorizations to those of a year ago should be the same for reporting and non-reporting places. Imputations for annual demolition permits occur only if a permit issuing jurisdiction does not report. Demolition permits are then imputed from the prior year's total. Change to the residential housing stock as measured by building and demolition permit records is limited since these records do not reflect construction or demolition activity outside of areas subject to local permit requirements. For the nation as a whole, approximately 5 percent of all privately owned housing units are constructed in areas not requiring building permits. However, this proportion varies greatly from state to state. Therefore, coverage adjustment factors have been developed to compensate for the lack of complete geographic coverage.