The enumerator determined the condition of the dwelling 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 "deterioration" and "inadequate original construction."

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.

Available vacant units.--This category provides a measure of vacant dwelling units which are on the housing market for year-round use. It consists of units which are for year-round use, are not dilapidated, and are being offered for rent or sale. Excluded are seasonal units, dilapidated units, and units already rented or sold or not on the rental or sale market for other reasons. The count of available vacancies constitutes a more effective measure of the supply of vacant housing than does the count of total vacancies. This category is comparable with the 1950 category "Nonseasonal not dilapidated, for rent or sale."

The category "For rent" consists of vacant units offered for rent as well as those being offered both for rent and for sale. The category "For sale" is limited to units for sale only. If a unit was located in a multi-unit 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, in a 2- or 3-dwelling-unit structure which was for sale, the unit intended to be occupied by the owner was reported as for sale.

Vacant units rented or sold.--This group consists of year-round not dilapidated vacant units 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 Census, 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 not dilapidated units 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; temporarily used for storage; and temporarily Occupied by persons who have a usual place of residence elsewhere. In the 1950 Census, 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.

Number of rooms.--All rooms which are to be used, or are suitable for use, as living quarters were counted in determining the number of rooms in the dwelling unit. Included are kitchens, bedrooms, dining rooms, living rooms, and permanently enclosed sunporches of substantial size; and finished basement or attic rooms, recreation rooms, or other rooms suitable for use as living quarters. A 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 dwelling units equally, onehalf 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 3-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 1-room apartment, therefore, was reported as having no bedroom. Also, space which could be made into bedrooms (the upper floor of a 1-story house, for example) was not counted as a bedroom unless it was finished off and suitable for use as living quarters.

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Number of dwelling units in structure.--A structure either stands by itself or has vertical walls dividing it from all other structures. The count of dwelling 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 one of a row of three or more adjoining structures, or is a structure attached to a nonresidential structure; while a semi detached structure is one of two ad joining 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.

The statistics reflect the number of vacant dwelling units classified by the number of dwelling units in the structure in which they are located, rather than on the number of residential structures that contain vacant units.

In the 1955 survey, data were obtained on the number of dwelling units in the structure, regardless of the type of structure (detached, attached,

or semidetached) in which the unit was located. In the 1950 Census, statistics for 1- and 2-dwellingunit structures are shown by type of structure as well as by number of dwelling units in the structure. Figures for 1950 "1 dwelling unit" category, for the tables in this report, were derived by combining "1 dwelling unit, detached," "1 dwelling unit, attached," and an estimated portion of the "1 and 2 semidetached" category which represents units in semidetached structures containing only 1 dwelling unit. Similarly, the figures for the "2 dwelling unit" category were derived by combining the "12 dwelling unit, other" category and the remaining portion of the "1 and 2 semidetached" category.

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Duration of vacancy.--The length of time dwelling 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 remains unoccupied but 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 vacancy, that is, when construction had reached the point that all exterior windows and doors were installed and final usable floors were in place.

Monthly rent.--The monthly rent is the amount asked for the unit at the time of enumeration, regardless of whether it is to include furniture, heating fuel, electricity, cooking fuel, water, or other services. If the amount of rent were to vary during the year, the rent reported was the monthly amount asked at the time of enumeration. The data on rent for this report are limited to nonfarm available vacant dwelling units for rent. Rent statistics are not provided for vacant farm dwelling units because of the difficulty of separating the rental for the dwelling unit from the rental for the entire farm unit.

The median monthly rent of the dwelling units 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 nonfarm available vacant units for rent.

Sale price of 1-dwelling-unit structures.--The sale price is the amount asked for the property, including the structure and its land. Value data are limited to vacant nonfarm units in 1-dwelling-unit structures, without business, and with only one dwelling unit included in the property. The statistics on sale price for this report are limited to nonfarm available vacant units for sale. Values for other available units for sale are not provided because they would reflect varying amounts for farm land, business uses, or for more than one dwelling unit in the property.

The median sale price of the dwelling units is the amount which divides the series into two equal parts, one-half of the units with prices higher than the median and the other half with prices 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.

sampling variability and may be expected to differ from results that would have been obtained from a complete count in which identical enumeration techniques were employed. The standard error is a measure of sampling variability. The chances are about 68 out of 100 that the difference due to sampling variability between an estimate and the figure that would have been obtained from a complete enumeration is less than the standard error. The chances are about 95 out of 100 that the difference is less than twice the standard error and about 99 out of 100 that it is less than 2 times the standard error.

SOURCE AND RELIABILITY OF DATA

The estimates for 1955 presented in this report are based on data obtained in connection with the monthly population sample survey of the Bureau of the Census. This sample is spread over 230 sample areas comprising 453 counties and independent cities. A total of 24,000 to 26,000 dwelling units and other living quarters were designated for the sample during each of the three months covered by the report. of this total, about 21,000 to 23,000 were occupied dwelling units, 2,000 were vacant dwelling units, and the remainder were units which had been converted to commercial use, had been demolished, etc., or were not living quarters within the scope of the Detailed information was obtained for each survey. vacant unit in the. sample.

The data for 1950 are based on the returns of the 1950 Census of Housing and represent the results of a complete enumeration.

Since the 1955 statistics presented in this report are based on a sample, they are subject to