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 1970 and 1969 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 if 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 rooïns 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."