For a more detailed explanation on condition of housing, see Series H-111 reports for quarters in 1968 or earlier. Also, see 1960 Census of Housing, Volume I, States and Small Areas.

A

Number of rooms. --All rooms which are used. or are suitable for use, as living quarters were counted in determining the number of rooms in the housing unit. Included are kitchens, bedrooms, dining rooms, living rooms, and permanently enclosed sunporches of substantial size; and finished basement or attic rooms, recreation rooms, suitable for use as living quarters. kitchenette or half-room which is partitioned off from floor to ceiling was counted as a separate room, but a combined kitchenette and dinette separated only by shelves or cabinets was counted as only one room. Not counted as rooms were bathrooms, strip or pullman kitchens, halls or foyers, alcoves, pantries, laundries, closets or storage space, and unfinished basement or attic rooms not suitable for living quarters.

The median number of rooms is the theoretical value which divides the housing units equally, one-half having more rooms and one-half having fewer rooms than the median. In the computation of the median, a continuous distribution was assumed. For example, when the median was in the three-room group, the lower and upper limits were assumed to be 2.5 and 3.5, respectively. Tenths were used in the computation of the median to permit comparisons.

Number of bedrooms.--Only rooms intended primarily to be slept in were counted as bedrooms. A bed-living room or a den intended primarily for purposes other than sleeping was not counted as a bedroom. A one-room apartment, therefore, was reported as having no bedroom.

Number of housing units in structure.-- A structure either stands by itself or has vertical walls dividing it from all other structures. The count of housing units in a structure is the total number of units in the structure, including both occupied and vacant units. A structure may be detached, attached, or semidetached. A detached structure has open space on all four sides; an attached structure is one of a row of three or more adjoining structures, or is a structure attached to a nonresidential structure; while a semidetached structure is one of two adjoining residential structures, each with open space on the remaining three sides. In apartment developments, each building with open space on all sides is considered a separate structure. In the tabulations, occupied trailers are included in the category "one housing unit" in structure.

The statistics reflect the number of housing units in the structure in which they are located,

rather than the number of residential structures. In the quarterly surveys, data were obtained on the number of housing units in the structure, regardless of the type of structure (detached, attached, or semidetached) in which the unit was located.

Year structure built.--"Year built” refers to the date the original construction of the structure was completed, and not to any later remodeling, addition, or conversion. The figures on the number of units built during a given period relate to the number of units in existence at the time of enumeration. The figures reflect the number of units constructed during a given period plus the number created by conversions in structures originally built during that period, minus the number lost in structures built during the period. Losses occur through demolition, fire, flood, disaster; change to nonresidential use; or merger to fewer housing units.

Data on year built are more susceptible to errors of response and nonreporting than data on many of the other items. In most cases, the information was given according to memory or estimates of the occupants of the structure or of other persons who had lived in the neighborhood a long time.

Duration of vacancy.-- The length of time a housing unit was vacant was computed from the day the unit became vacant until the day of enumeration. It should be noted that the time period is not the total time a unit has been in a particular vacancy status, but it is the duration of vacancy up to the day of enumeration. For newly constructed units, it represents the time period since the date when the unit was considered a vacant housing unit, that is, when construction had reached the point that all exterior windows and doors were installed and final usable floors were in place.

The time intervals used in the tables represent full months, calculated from a date in the month to the same date the following months. For example, if the unit became vacant on January 29 and was still vacant on the day of enumeration, March 20, the time reported would be "1 up to 2 months," meaning that the unit had been vacant for more than 1 month but less than 2 months. Or if the unit became vacant on February 25 and was still vacant on March 20, the time reported would be "less than 1 month."

Plumbing facilities. --Housing units "with all facilities" consist of those which have: Both a flush toilet and a bathtub or shower inside the structure for the exclusive use of the intended occupants of the unit, and hot running water.

Units "lacking facilities" consist of those which lack one or more of the plumbing facilities or which lack exclusive use of these facilities.

Facilities were considered "inside the structure" if they were located within the housing unit or elsewhere in the structure. Facilities are for exclusive use if they are used, or intended for use, by only the occupants of one housing unit.

A housing unit was considered as having hot running water whether it was available the year round or only part of the time. For example, hot running water may be available only during the heating season or at various times during the week.

Contract rent.-- For renter-occupied units, the contract rent is the monthly rent agreed upon regardless of any furnishings, utilities, or services that may be included. For vacant units, rent is the amount asked for the unit at the time of enumeration; the amount may differ from the rent contracted for when the unit is occupied. As in the 1960 census, the statistics exclude rents for renter-occupied farm housing units in rural territory and rents for vacant units on places of 10 acres or more in rural areas. The statistics in the reports for 1960 or earlier exclude rental vacancies in rural areas which were classified as farm by the 1950 definition (the classification depending on the reply to the question "Is this house on a farm or ranch?"). Data for such units are excluded because of the difficulty of separating the rental for the housing unit from the rental for the land.

The median monthly rent is the rent which divides the series into two equal parts, one-half of the units with rents higher than the median and the other half with rents lower than the median. In the computation of the median, a continuous distribution was assumed; and the limits of the class intervals were assumed to stand at the midpoints of the 1-dollar interval between the end of one of the rent groups and the beginning of the next. For example, the limits of the interval designated $30 to $39 were assumed to be $29.50 and $39.50.

Inclusion of utilities in rent.-- The utilities included in the inquiry were heat, light, cooking fuel, and water. The statistics reflect whether all or not all of these utilities are provided for in the amount of rent asked at the time of enumeration, not what could be provided for more or less rent. Data on the inclusion of utilities are limited to the vacant units for which rent is reported. No data on utilities are collected for renter-occupied units.

Value.--Value is the respondent's estimate of how much the property would sell for on the current market. For vacant units, value is the sale price asked for the property at the time of enumeration and may differ from the price at which the property is sold. Statistics on value for owner-occupied units and sale price asked for vacancies available for sale are limited to units in 1-housing unit structures, without business, and with only one housing unit on the property. Statistics on value also exclude occupied trailers.

As in the 1960 census, the statistics in this report are for owner-occupied and vacant forsale units in urban areas and those in rural areas which are located on places of less than 10 acres; thus units in rural areas on places of 10 acres or more are excluded. The statistics in the reports for 1960 or earlier exclude homeowner vacancies in rural areas which were classified as farm by the 1950 definition (the classification depending on the reply to the question "Is this house on a farm or ranch?”). Data for such units are excluded because they would reflect varying amounts for land, business uses, or for more than one housing unit on the property.

The median value or sale price is the amount which divides the series into two equal parts, onehalf of the units with values higher than the median and the other half with values lower than the median. The median was computed on the basis of more detailed tabulation groups than are shown in the tables and was rounded to the nearest hundred dollars.

Urban-rural residence.-- The territory classified as urban is the same as that in the 1960 census. Urban housing comprises all units in (a) places of 2,500 inhabitants or more incorporated as cities, boroughs, villages, and towns (except towns in New England, New York, and Wisconsin); (b) the densely settled urban fringe, whether incorporated or unincorporated, of urbanized areas; (c) towns in New England and townships in New Jersey and Pennsylvania which contain no incorporated municipalities as subdivisions and have either 25,000 inhabitants or more or a population of 2,500 to 25,000 and a density of 1,500 persons or more per square mile; (d) counties in States other than the New England States, New Jersey, and Pennsylvania that have no incorporated municipalities within their boundaries and have a density of 1,500 persons or more per square mile; and (e) unincorporated places of 2,500 inhabitants or more. The remaining units are classified as rural.

Source of data. --The estimates presented in this report are based on data obtained from two surveys conducted by the Bureau of the Census. Data concerning vacancy rates and tenure of occupied housing units are from the monthly sample of the Current Population Survey (CPS). Characteristics of occupied housing units are from the Quarterly Household Survey (QHS).

The Current Population Survey sample is spread over 449 areas comprising 863 counties and independent cities with coverage in each of the 50 States and the District of Columbia. Approximately 50,000 occupied households are designated for interview each month; of this number 2,250 occupied units, on the average, are visited but interviews are not obtained because the occupants are not found at home after repeated calls or are unavailable for some other reason. In addition ot the 50,000, there are also about 8,500 sample units in an average month which are visited but are found to be vacant or otherwise not to be interviewed. Data on vacancy rates and tenure of occupied units for the first quarter 1971 are averages over the 3 months, January, February, and March.

The data concerning characteristics of occupied housing units are from the Quarterly Household Survey (QHS). This sample is spread over 235 areas, comprising 484 counties and independent cities. The figures for the first quarter 1971 are based on the average of four quarterly estimates produced from interviews conducted in April, July, and October of 1970 and January of 1971. The estimates for the four quarters are each based on a one-third sample of the QHS households. Estimates for a full QHS sample are based on interviews conducted in approximately 11,500 households. These households come from a larger sample of 16,000 occupied housing units. The smaller sample is chosen by identifying the households with annual family income less than $6,000 and interviewing a sample of one-half of these. The units with income less than $6,000 retained in the sample are given twice the weight of the other units in the sample to compensate for

this subsampling. In addition to the 11,500 occupied housing units interviewed, about 1,000 occupied units are visited but interviews are not obtained because the occupants are not found at home after repeated calls or are unavailable for some other reason. There are also 2,000 units in the QHS sample visited but found to be vacant or otherwise not to be enumerated. Data for these vacant units are not included in the figures for this report.

The estimating procedures used for the QHS involve the inflation of the weighted sample results to independent estimates of the number of owner-occupied and renter-occupied housing units by urban and rural residence based on data from the Current Population Survey (CPS). These independent estimates have a lower sampling error due to the larger sample size and because other current independent estimates of the population of the United States are employed in the CPS estimation procedure.

Reliability of the estimates.--Since the estimates are based on a sample, they may differ somewhat from figures obtained if a complete census had been taken using the same schedules, instructions, and enumerators. As in any survey work, the results are subject to errors of response and of reporting as well as being subject to sampling variability.

The standard error is primarily a measure of sampling variability, that is, of the variations that occur by chance because a sample rather than the whole of the population is surveyed. As calculated for this report, the standard error also partially measures the effect of response and enumeration errors but does not measure any systematic biases in the data. The chances are about 68 out of 100 that an estimate from the sample would differ from a complete census figure by less than the standard error. The chances are about 95 out of 100 that the difference would be less than twice the standard error.

Comparison of characteristics of the vacancies for the first quarter 1971 with previous quarters (Series H-111, Nos. 1 to 63) reveals that many of the differences are small. A small difference,