This supplement contains quarterly and annual statistics on new mobile homes for the United States and the four Census regions. Table S1 shows number of new mobile homes placed for residential use. Table S2 shows average sales price for those new mobile homes placed. Table S3 shows inventory of mobile homes on dealers' lots at the end of each period.

For these series, a mobile home is defined as a moveable dwelling, 10 feet or more wide and 35 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 double wides, which are counted as single units, and expandable mobile homes. Excluded are travel trailers, motor homes and modular housing.

The series of shipments of mobile homes shown in table 8 of this report are estimates of new mobile homes shipped by manufacturers each month. These estimates differ from mobile home placements in several ways: they include some units which may be used for nonresidential purposes, such as units used as offices at construction sites, school rooms and temporary bank facilities; shipments to dealers may not be placed in the same month as they are shipped; and the definition of a mobile home used by the Manufactured Housing Institute, which provides the shipments estimates, differs slightly from the definition for mobile home placement statistics in that the dimension requirement used by the Institute is a minimum of 8 feet wide or 32 feet long.

SOURCE OF INFORMATION

These statistics are derived from the Survey of New Mobile Home Placements conducted by the Bureau of the Census and sponsored by the Department of Housing and Urban Development. For this survey, a sample of business establishments dealing in new mobile homes are asked to report the number of new mobile homes they placed for residential use in the survey period. These include units sold and units leased. They also are asked to report the total value of sales of the units including estimates for those leased, and the number of new mobile homes on their lot at the end of the period.

The sample of establishments in the survey is selected using probability sampling methods. First, a sample of geographic areas is selected. Then within each sampled area, a sample of dealers is selected from a list of business establishments that sell, rent, lease or have the potential of selling new mobile homes. The list of dealers is updated annually.

Estimates are made based on data received from sampled dealers. Adjustments are made for nonrespondents and for new

mobile home dealers coming into existence after the sample is selected. Adjustments are also made to account for establishments which were not given a chance of selection when the sampling frame was created.

NOTE: Estimates have been revised to reflect the following: 1. results from the 1977 updating of the sample frame, and 2. corrections of response errors.

RELIABILITY OF ESTIMATES

Since the statistics in this report are estimates from a sample survey, they differ from the results that would have been obtained from a complete census using the same schedules and procedures. Estimates based on a sample are subject to both sampling and nonsampling errors. Sampling errors occur because observations are made on a particular sample rather than the entire population. Nonsampling errors can be attributed to many sources: inability to obtain information about all cases in the sample; definitional problems; differences in the interpretation of questions; inability or unwillingness by respondent to provide correct information and errors made in processing data. Estimates of size of sampling errors are provided by the relative standard error, which measures the variation that occurs by chance because a sample rather than the whole population is surveyed. No explicit measures of the effects of nonsampling errors are available. However, it is believed that most of the important response and operational errors were detected in the course of reviewing the data for reasonableness and consistency. As derived for this report, the estimated relative standard errors include part of the effect of nonsampling errors but do not measure any systematic biases in the data.

The particular sample selected for the Survey of New Mobile Home Placements is one of a large number of similar probability samples that, by chance, might have been selected under the same specifications. Estimates derived from the different samples would differ from each other. The relative standard error of a survey estimate is a measure of the variation among the estimates from all possible samples and thus is a measure of the precision with which an estimate from a particular sample approximates the average results of all possible samples.

Average relative standard errors for quarterly estimates of mobile home placements, inventories and average sales price have been computed from the sample data. They are shown in the tables. See Appendix A in this report for a more detailed description of sampling variability.

DEFINITIONS

A housing start is defined as the start of construction of a new housing unit, when located within a new building which is intended primarily as a house keeping residential building designed for nontransient occupancy. Start of construction for private housing units is defined as the beginning of excavation for the footings or foundation of a building; for public housing units it is defined as when the construction contract is awarded. All housing units in a multi-family building are counted as being started when excavation for the building is started.

A housing unit is a single room or group of rooms intended for occupancy as separate living quarters by a family, by a group of unrelated persons living together, or by a person living alone. Separate living quarters are those in which the occupants do not live and eat with any other persons in the structure and which have either (1) direct access from the outside of the building or through a common hall which is used or intended to be used by the occupants of another unit or by the general public; or (2) complete kitchen facilities for the exclusive use of the occupants.

A house keeping residential building is one consisting primarily of housing units. New housing starts exclude group quarters (such as dormitories and rooming houses), transient accommodations (such as transient hotels, motels, and tourist courts), mobile homes (trailers), moved or relocated buildings, and housing units created in an existing residential or nonresidential structure. However, in a building combining substantial residential and nonresidential floor areas, every effort is made to include the residential units in these statistics even though the primary function of the entire building is for nonresidential purposes.

Housing units, as distinguished from mobile homes, include conventional "stick built" units, prefabricated, panelized, componentized, sectional and modular units. Except for table 8, mobile homes-single wide and multi-wide-are excluded from the statistics. A mobile home is defined as a portable dwelling constructed to be towed on its own chassis and designed for use without a permanent foundation; it is manufactured with the running gear an integral part of the unit and can be towed from site to site.

Publicly owned housing includes housing units in buildings for which construction contracts were awarded by Federal, State or local governments. Units in structures built by private developers for sale upon completion to local public housing authorities under the U.S. Department of Housing and Urban Development "Turnkey" program are classified as private housing.

The statistics, by type of structure, refer to the structural characteristics of the building. The one-unit structure category includes fully detached, semidetached (semiattached, side-byside), rowhouses, and townhouses. In the case of attached units, each must be separated from the adjacent unit by an unbroken ground-to-roof party wall in order to be classified as a oneunit structure. Units built one on top of another and those built side-by-side which do not have an unbroken ground-toroof party wall and/or have common facilities, i.e., attic, basement, heating plant, plumbing, etc., are classified by the number

of units in the structure (ie., two-unit structure, three-unit structure, etc.). In these statistics, apartment buildings are defined as buildings containing five units or more. Apartments in a conventional-type apartment building may share a common basement, heating plant, stairs, entrance halls, and water supply and sewerage disposal facilities. Townhouse apartments, though attached, are not separated by an unbroken ground-to-roof party wall and share some interstructural facilities such as water supply, sewerage disposal, etc.

Ownership is not the criterion for structural classifications in this report. A condominium apartment building is classified with apartment buildings in structures with five units or more despite the fact that each unit is individually owned. Condominium townhouses may be in the one unit category if each unit is separated from its neighbor by an unbroken ground to roof party wall (no commonly shared interstructural facilities), or in the multiunit building categories if they are not separated from each other by an unbroken ground-to-roof party wall (share interstructural facilities).

The standard census geographic regions are used in the tables of this report. States contained in each region are as follows: Northeast-Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, and Pennsylvania; North Central-Ohio, Indiana, Illinois, Michigan, Wisconsin, Minnesota, Iowa, Missouri, North Dakota, South Dakota, Nebraska, and Kansas; South-Delaware, Maryland, District of Columbia, Virginia, West Virginia, North Carolina, South Carolina, Georgia, Florida, Kentucky, Tennessee, Alabama, Mississippi, Arkansas, Louisiana, Oklahoma, and Texas; WestMontana, Idaho, Wyoming, Colorado, New Mexico, Arizona, Utah, Nevada, Washington, Oregon, California, Alaska, and Hawaii.

The distribution of housing starts between units inside and outside Standard Metropolitan Statistical Areas (SMSA's) is based on the definitions published by the Office of Management and Budget in Standard Metropolitan Statistical Areas. Data for the period beginning January 1976 are based on the 1974 definitions as amended August 1975; data for the period January 1975-December 1975 are based on the 1967 definitions, as amended April 1974; data for the period January 1974December 1974 are based on the 1967 definitions, as amended November 1973; data for April 1973-December 1973 are based on the 1967 definitions as amended February 1973; data for April 1968-March 1973 are based on 1967 defintions.

HOUSING STARTS COMPILATION

The compilation of the housing starts series is a multistage process. First, an estimate is made monthly of the number of housing units for which building permits have been issued in all 14,000 permit-issuing places (table 6). The preliminary estimate of building permit authorizations is based on a sample of 2,800 permit-issuing places. The revised estimate is based on a sample of 6,800 of these 14,000 jurisdictions.

Second, within 137 sampled land areas (counties or groups of counties) an independent survey is conducted monthly in a subsample of the permit-issuing places (approximately 950)