Except for the instances noted below, the concepts and definitions used in the quarterly surveys are identical with those used in the 1960 census.

Standard metropolitan statistical area (SMSA).-Except in New England, an SMSA is a county or group of contiguous counties which contains at least one city of 50,000 inhabitants or more, or "twin cities" with a combined population of at least 50,000, the smaller of which must have at least 15,000. In addition to the county, or counties, containing such a city or cities, contiguous counties are included in an SMSA if, according to certain criteria, they are essentially metropolitan in character and are socially and economically integrated with the central city. In New England, SMSA's consist of towns and cities, rather than counties. A more detailed discussion of the criteria used to define SMSA's is given in 1960 Census of Housing, Volume I, States and Small Areas.

The statistics for inside SMSA's and outside SMSA's presented for the second quarters 1971 and 1970 relate to the areas (212) designated SMSA's at the time of the April 1960 Census. Prior to the second quarter 1962, the statistics related to the areas (168) designated SMA's at the time of the 1950 census For a list of the 212 SMSA's and their constituent parts, refer to the individual chapters (or Series HC(1) reports) in the 1960 Census of Housing, Volume I, States and Small Areas; or to the 1960 Census of Population, Volume I, Number of Inhabitants. For a list of the 168 areas and their constituent parts, refer to the individual chapters (or bulletins) in the 1950 Census of Housing, Volume I, General Characteristics; or to the 1950 Census of Population, Volume I, Number of Inhabitants, or Volume II, Characteristics of the Population, Part I, United States Summary.

Housing unit.--Beginning with the second quarter 1960, the 1960 census housing unit concept was used to enumerate separate living quarters. Prior to that time, separate living quarters were enumerated according to the 1950 dwelling unit definition. The major difference between the two is not in content but in sharpening of the criteria by which separate units are identified. It is expected that the housing unit concept will yield better coverage of both occupied and vacant living quarters than the dwelling unit concept. Although no statistical measure of the effect of the change is available at this time, it is believed to be too small to affect the vacancy rates.

A group of rooms or a single room is regarded as a housing unit when it is occupied as separate living quarters, that is, when the oc

cupants do not live and eat with any other persons in the structure, and there is either (1) direct access from the outside or through a common hall, or (2) a kitchen or cooking equipment for the exclusive use of the occupants.

Vacant living quarters intended for occupancy as separate living quarters and those that meet the physical criteria defined above are separate housing units. Because it is customary in some localities for occupants to furnish their own cooking equipment, vacant units without a kitchen or cooking equipment are considered to have such equipment if the last occupants had cooking equipment.

Living quarters of the following types 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.

Quarters for roomers or boarders having shared living arrangements are excluded from the housing inventory if there are five or more such rooms; they are combined as one housing unit if there are four or fewer such rooms.

Trailers, tents, and boats are excluded if vacant, used for business, or used for extra sleeping space or vacations.

Dwelling unit. 1950.-- The 1950 dwelling unit was defined as follows: A group of rooms occupied as separate living quarters was a dwelling unit if it had separate cooking equipment or if it constituted the only living quarters in the structure. Each apartment in a regular apartment house was a dwelling unit even though it may not have had separate cooking equipment. Apartments in residential hotels were dwelling units if they had separate cooking equipment or consisted of two or more rooms.

Vacant quarters intended for occupancy as separate living quarters and met the physical criteria defined above were separate dwelling units. Vacant units were considered as having cooking equipment if they were equipped with such equipment or if the last occupants had cooking equipment.

In general, living quarters of the types excluded from the housing unit inventory were excluded from the dwelling unit inventory.

Occupied housing units.--A housing unit is occupied it a person or group of persons was living in it at the time of enumeration or if the occupants were only temporarily absent, as for example, on vacation. The persons living in the unit must consider it their usual place of residence or have no usual place of residence elsewhere. The count of occupied housing units is the same as the count of households.

Units occupied by persons with usual residence elsewhere.-- A housing unit which is occupied temporarily by persons who usually live elsewhere is enumerated as a vacant unit provided the usual place of residence is held for the household and is not offered for rent or for sale. For example, a beach cottage occupied at the time of enumeration by a family which has a usual place of residence in the city is included in the count of vacant units. Their house in the city would be reported "occupied" and would be included in the count of occupied units since the occupants are only temporarily absent.

Units occupied by persons with usual residence elsewhere are included with seasonal units or with year-round vacant units as dilapidated, or not dilapidated but held off the market, as the case may be.

Vacant housing units.--A housing unit (furnished or unfurnished) is vacant if no persons were living in it at the time of enumeration, except when its occupants were only temporarily absent. Dilapidated vacant units were included if they were intended for occupancy as living quarters; however, if the vacant unit was unfit for use and beyond repair so that it was no longer considered living quarters, it was excluded from the inventory. Vacant units to be demolished were excluded if unfit or if there was positive evidence, such as a sign or mark on the house or in the block, that the unit was to be torn down. New units not yet occupied were enumerated as vacant housing units if construction had proceded to the point that all the exterior windows and doors were installed and final usable floors were in place; otherwise, potential units under construction were not included. Unoccupied units held off the market for various reasons and units recently rented or sold but not yet occupied are considered vacant.

Vacant sleeping rooms in lodginghouses, transient accommodations, barracks, and other quarters not defined as housing units are not included in the statistics in this report. (See section on "Housing unit.")

Year-round vacant units.-- Year-round units are those intended for occupancy at any time of the year, even though they may not be in use the year round. In resort areas, a housing unit which

is usually occupied on a year-round basis was considered a year-round unit. On the other hand, a housing unit located in the closely built-up area of a nonresort city was considered a "year round" unit even though it may be occupied only part of the year. As indicated above, year-round units temporarily occupied by persons with usual residence elsewhere are included with year-round vacant units.

Seasonal vacant units.--Seasonal housing units are those intended for occupancy during only a season of the year and are found primarily in resort areas. In farm areas, housing units used for only a portion of the year to house migratory workers employed during the crop season are classified as seasonal.

Seasonal units comprise unoccupied seasonal units and seasonal units temporarily occupied by persons with usual residence elsewhere. Units in resort areas occupied by persons who considered the unit their usual place of residence or had no other place of residence are classified as occupied. (See also section on "Occupied housing units.")

Available vacant units.--The categories "available for rent" and "available for sale only" provide a measure of vacant housing units which are on the market for year-round occupancy, are in either sound or deteriorating condition, and are being offered for rent or for sale.

To describe the rental and sale market, the measure of units available for rent is expressed as a percentage of the total rental inventory and the measure of units available for sale is expressed as a percentage of the total homeowner inventory. In the analysis of the total inventory and total vacant units, percentages are based on total housing units.

Beginning with Series H-111 report No. 55, additional measures are given which describe the available vacancy supply in terms of selected characteristics of the rental and homeowner inventories. Vacancy ratios are provided by monthly rent levels, asking price, year built, number of rooms, number of units in structure, and plumbing facilities.

Vacant units available for rent. --This group consists of available vacant units offered for rent and those offered "for rent or sale."

Vacant units available for sale only.--This group is limited to units for sale only; it excludes` units "for rent or sale." If a unit was located in a multiunit structure which was for sale as an entire structure and if the unit was not for rent, it was reported as "held off market." However, if the individual unit was intended to be occupied by the new owner, it was reported as "for sale."

Vacant units rented or sold.--This group consists of year-round vacant units in sound or deteriorating condition which have been rented or sold but the new renters or owners have not moved in as of the day of enumeration. In the 1950 statistics, such units are shown in combination with year-round not dilapidated vacant units held off the market.

Vacant units held off the market.--Included in this category are year-round units in sound or deteriorating condition which were vacant for reasons other than those mentioned above: For example, held for occupancy of a caretaker, janitor, and the like; held for settlement of estate; held for personal reasons of the owner; and temporarily occupied by persons who have a usual place of residence elsewhere. In the 1950 statistics, such units are shown in combination with year-round not dilapidated vacant units, rented or sold, as "nonseasonal not dilapidated, not for rent or sale" units.

Rental vacancy rate.--The percentage relationship of the vacant units available for rent to the total rental inventory is termed the rental vacancy rate. It is computed by dividing the number of vacant units available for rent by the total rental units. The total rental units consist of the renter-occupied units, vacant units rented but not yet occupied at the time of enumeration, and the vacant units available for rent. Vacant units that are dilapidated, seasonal, or held off the market are excluded.

Homeowner vacancy rate. --The percentage relationship between the vacant units available for sale and the total homeowner inventory is termed the homeowner vacancy rate. It is computed by dividing the number of vacant units available for sale by the total homeowner units. The total homeowner units consist of the owner-occupied units, vacant units sold and awaiting occupancy, and the vacant units available for sale. Vacant units that are dilapidated, seasonal, or held off the market are excluded.

Vacancy rates by selected characteristics.-These ratios express the relationship between subclasses of vacant available housing units and rental and homeowner units that have a common characteristic.

Selected vacancy rates in rental units are computed by dividing the number of available vacant for-rent units in the specified category by the total rental units in that group. The total rental units consist of the renter-occupied units and the vacant for-rent units with the common characteristic. Similarly, vacancy rates in specific types of homeowner units are computed by dividing the total number of vacancies for sale

in the selected group by the sum of the total owner-occupied and vacant for-sale units in the same group.

Tenure.-- A unit is owner occupied if the owner or co-owner lives in the unit, even if it is mortgaged or not fully paid for. All other occupied units are classified as "renter occupied" whether or not cash rent is paid. Thus, units occupied in exchange for services rendered and units provided without payment of cash rent are "renter occupied."

Condition of housing unit.--In this survey, the structural condition of a housing unit is obtained for only vacant units. Beginning the first quarter 1961, condition was measured according to the concept used in the 1960 census. Three categories were used: Sound, deteriorating, and dilapidated. In preceding quarters and in 1950, two categories were used: Not dilapidated, or dilapidated. The category "sound or deteriorating" is assumed to be equivalent to the category "not dilapidated."

Sound housing has no defects, or only slight defects which are normally corrected during the course of regular maintenance.

Deteriorating housing needs more repair than would be provided in the course of regular maintenance. It has one or more defects of an intermediate nature that must be corrected if the unit is to continue to provide safe and adequate shelter.

Dilapidated housing does not provide safe and adequate shelter. It has one or more critical defects, or has a combination of intermediate defects in sufficient number to require extensive repair or rebuilding, or is of inadequate original 'construction.

The enumerator determined the condition of the housing unit on the basis of his own observation. He was instructed to appraise the condition of units uniformly, regardless of the neighborhood. The enumerator was provided with detailed written instructions and with pictures illustrating the concepts "sound," "deteriorating," and "dilapidated."

Although the enumerator was provided with detailed oral and written instructions and with visual aids, it was not possible to eliminate completely the element of judgment in the enumeration of this item. It is possible that some enumerators obtained too large or too small a count of dilapidated units. However, with the large number of enumerators involved, it is likely that such deviations tend to be offsetting.