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COLLECTION OF DATA

Data collection forms.-Two basic types of forms were used for collecting data in the 1960 Census--the forms which respondents were asked to fill and the forms used by the enumerator to record the information for processing.

Advance Census Report and Household Questionnaire.-Both the Advance Census Report (ACR) and the Household Questionnaire were self-enumeration forms. The ACR contained items which were to be reported for all occupied housing units and was used on a nationwide basis. The Household Questionnaire contained questions which were asked on a sample basis and was used in the more populous areas.

FOSDIC schedules.-The FOSDIC schedules are forms specially designed for electronic data processing Two basic types were used-a "complete-count" FOSDIC schedule and a "sample" FOSDIC schedule. The complete-count FOSDIC schedule contained items enumerated for every housing unit. Information was either transferred from the ACR or recorded on the schedule during direct interview. This schedule was used also for recording information not called for on the ACR, namely access to unit (which is pertinent to the identification of a housing unit), condition of the unit, and information about vacant units. The sample FOSDIC schedule contained items that were enumerated on a sample basis. Information was either transferred from the Household Questionnaire or recorded on the schedule during direct interview.

Enumeration procedures.-Before the enumeration began, the Post Office Department delivered an ACR to households on postal delivery routes in all parts of the United States. This form contained questions which were to be answered for every occupied housing unit. Household members were requested to fill the ACR and have it ready for the enumerator when he called.

Two-stage and single-stage procedures.-The enumeration process involved two basic procedures. In the more populous areas of the United States (with approximately 82 percent of the population and 35 percent of the land area), a "two stage" enumeration procedure was used. In the firststage visit to the housing unit (Stage I) the enumerator transferred information froin the ACR to the complete-count FOSDIC schedule. If the ACR was not filled for the unit or if the form had omissions or inconsistencies, the enumerator was instructed to ask the questions and record the answers directly on the FOSDIC schedule. If the household was in the sample, the enumerator left a Household Questionnaire to be filled and mailed promptly to the local census office. It was also necessary for the Stage I enumerator to transfer the complete-count information for each sample household to its sample FOSDIC schedule. This schedule was then given to the Stage II enumerator.

In the second stage (Stage II), the enumerator transferred the information supplied by the household from the Household Questionnaire to the sample FOSDIC schedule. If the enumerator found that the questionnaire was incompletely filled or had not been mailed, or if he detected answers containing obvious inconsistencies, he obtained the missing information by personal visit or by telephone and recorded it directly on the sample FOSDIC schedule (or on the Household Questionnaire and then on the FOSDIC schedule).

In the rest of the United States, where approximately onefifth of the population lives, a "single stage" enumeration procedure was used.' As in the two-stage areas, the enumera

7 States enumerated completely on a single-stage basis were: Alaska, Arkansas, Hawaii, Idaho, Mississippi, Montana, Nevada, New Mexico, North Dakota, South Dakota, and Wyoming. States enumerated partly, but not completely, on a single-stage basis were: Alabama, Arizona, California, Colorado, Florida, Georgia, Kansas, Kentucky, Louisiana, Maine, Michigan, Minnesota, Nebraska, Oklahoma, Oregon, Texas, Utah, Washington, and

tor visited the housing unit and transferred information from the ACR to the complete-count FOSDIC schedule. If the ACR was not filled for the unit or if the form had omissions or inconsistencies, the enumerator was instructed to ask the questions and record the answers directly on the FOSDIC schedule. For each unit in the sample, the enumerator asked the questions for the sample items and recorded the answers directly on the sample FOSDIC schedule. The Household Questionnaire was not used in single-stage areas.

Thus, the "two stage" and "single stage" procedures differed only in the method of obtaining information for the sample items.

Methods of obtaining information.-Information for the housing items was obtained through self-enumeration, direct interview, and observation. The method used for each item and the enumeration form on which the item appears are indicated in the section on "Definitions and explanations."

Procedure for vacant units.--In both two-stage and singlestage areas, information for vacant units was obtained by the enumerator and recorded directly on the FOSDIC schedule. Information was obtained from owners, landlords, neighbors, or other persons presumed to know about the unit. For each vacant unit in the sample, the enumerator in single-stage areas completed the sample FOSDIC schedule at the same time he obtained the complete-count information. In two-stage areas, the Stage II enumerator completed the sample FOSDIC schedule.

Listing procedure.-As a means toward obtaining complete coverage of housing units, the enumerator in both two-stage and single-stage areas listed each occupied and vacant unit on his first visit to the unit for information from the ACR. He was instructed to canvass each block, street, or road in a systematic manner and to record the address, name of head (of occupied unit), time to call if a callback was required, and other pertinent information about the visit. A Listing Book was used for this purpose.

Field review.-One of the more important innovations in the 1960 Census was a series of regularly scheduled "field reviews" of the enumerator's work by his crew leader or by a field reviewer. This operation was designed to assure at an early stage of the work that the enumerator was performing his duties properly and had corrected any errors he had made. Moreover, the completeness of coverage of housing units was checked in various ways, including for the first time a comparison of addresses listed by the enumerator with an advance partial listing of addresses prepared by the supervisor.

PROCESSING OF DATA

Electronic processing.— Although mechanical equipment was widely used in the 1950 and 1960 Censuses in the editing, coding, and tabulating of housing data, the procedures adopted in 1960 differed in several important respects from those used in 1950. The procedural changes reflected, in large part, the shift from other mechanical equipment to electronic equipment, which had been applied to the processing of housing information on a relatively limited scale in 1950.

In 1960, the enumerator had recorded housing information by marking appropriate circles on FOSDIC schedules. To process the data, (1) the schedules were sent to the central processing office in Jeffersonville, Indiana, where they were microfilmed; (2) the microfilm was then sent to Washington where the markings were converted to signals on magnetic tape by FOSDIC (Film Optical Sensing Device for Input to Computers); (3) the tape was processed by an electronic computer, which edited, coded, and tabulated the data; (4) a high-speed electronic printer printed the numbers and captions on sheets to which preprinted titles were added, and the tables were repro

In 1950, the enumerator had recorded housing information by marking a precoded check box or writing in numerical answers. To process the data, (1) clerks punched a card for each unit containing the codes for the housing characteristics; (2) the punchcards were edited, coded, and tabulated by conventional tabulators for all the 1950 housing reports except Volume II, for which electronic equipment was used for the tabulations; (3) the tables were typed manually on sheets with preprinted stubs and partially preprinted captions, and the tables were reproduced by offset printing.

The extensive use of electronic equipment in the 1960 Census ensured a more uniform and more flexible edit than could have been accomplished manually or by less intricate mechanical equipment. In the editing operations, allocations were made for nonresponses and inconsistencies. Moreover, the use of FOSDIC completely eliminated the cardpunching operation and thereby removed one important source of error in the published statistics; the new types of error introduced by the use of FOSDIC were probably minor by comparison.

The electronic computer made it possible to do much more complex editing and coding than in earlier censuses and to assure consistency among a larger number of interrelated items. For example, the computer assigned a code to each housing unit for one of seven categories of condition and plumbing facilities; to determine this code in some instances required the scanning of entries in four items, where a full cross-classification of the items would involve approximately 36 combinations of categories. At the same time, the greater capacity of the computer permitted the keeping of a detailed record of the extent of computer editing.

In 1960, practically all the editing and coding operations on the housing schedules were accomplished by electronic equipment. The only schedules examined manually (after the field review and inspection) were those flagged by the computer for clerical review because the number of corrections made exceeded the tolerances that were established. In 1950 also, much of the editing and coding was accomplished by mechanical equipment, including electronic equipment for some tabulations. A few specified items on the housing schedules in 1950 were examined manually, and corrected when necessary, before the schedules were processed mechanically.

Editing. In a mass statistical operation, such as a national census, human and mechanical errors occasionally arise in one form or another, such as failure to obtain or record the required information, recording information in the wrong place, misreading position markings, and skipping pages. These were kept to a tolerable level by means of operational control systems. Nonresponses and inconsistencies were eliminated by using the computer to assign entries and correct inconsistencies. In some cases, missing and inconsistent entries resulted from poor markings which were unreadable or were misread by FOSDIC. In general, few assignments or corrections were required, although the amount varied by subject and by enumerator.

Whenever information was missing, an allocation procedure was used to assign an entry, thereby eliminating the need for a "not reported" category in the tabulations. The assignment was based on related information reported for the housing unit or on information reported for a similar unit in the immediate neighborhood. For example, if tenure for an occupied unit was omitted but a rental amount was reported, the computer automatically edited tenure to "rented." On the other hand, if the unit was reported as "rented" but the amount of rent was missing, the computer automatically assigned the rent that was reported for the preceding renter-occupied unit. A similar procedure was used when the information reported

for the unit. For example, if a housing unit was enumerated as having "no running water" but having both a bathtub (or shower) and flush toilet for the exclusive use of the occupants of the unit, the computer edited water supply to "hot and cold water," a category considered to be consistent with the reported bathing and toilet facilities.

Specific tolerances were established for the number of computer allocations that was acceptable. If the number was beyond tolerance, the data were rejected and the original schedules were re-examined to determine the source of the error. Correction and reprocessing were undertaken as necessary and feasible. In some cases, the corrective action consisted simply of making darker shadings in the code circles. If the high number of allocations resulted from faulty entries or absence of entries on the schedules, the appropriateness of the computer allocations was considered and, in some instances, a manual allocation was substituted.

The extent of allocations for nonresponses and inconsistencies, including those resulting from poor markings, is shown for each item in appendix table A-1. The percentages reflect only the allocations made by the computer; they exclude any that were made in the field review of the census schedules and those that were made manually after they had been rejected by the computer. The table presents totals for the State, by inside and outside SMSA's, and totals for places of various population size groups. The base on which the percentage is computed is shown for each item. For most items, the percentages are based on all housing units or occupied housing units. In some instances, the base is a specific group of units. For example, a figure of 2.5 for "duration of vacancy" for places of 50,000 inhabitants or more means that answers to this question were supplied or edited for 2.5 percent of the vacant units available for rent or sale; the 2.5 percent is a combined figure for all places of 50,000 inhabitants or more in the State. Percentages are not shown if the item is not published for the specified areas.

In earlier censuses, assignments of acceptable entries for nonresponses and inconsistencies also were based on related information given for the units. In the absence of related information for the unit, either an acceptable code was assigned or the item was "not reported." If a code was assigned, it was made on the basis of distributions of characteristics from previous censuses or surveys. The use of electronic equipment in 1960 improved upon the procedure by making feasible the use of information implicit in the 1960 data being tabulated.

ACCURACY OF DATA

As explained above, information was obtained through selfenumeration and direct-interview procedures. The forms used by household members for self-enumeration were necessarily different from those used by the enumerator in direct interview, although the intent of the two types of forms was the same. The use of self-enumeration forms allowed household members to see the questions as worded and to consult household records to ascertain the correct answers. Furthermore, the self-enumeration forms provided brief but uniform explanations for some of the items and called attention to the response categories in a uniform manner. The less detailed wording for some items on the FOSDIC schedules was supplemented by the training and instructions given to the enumerators. The enumerators received standardized and formal training in canvassing their districts, in interviewing, and in filling out the schedules. During training, they used a workbook which contained practice exercises and illustrations. Filmstrips with accompanying narratives and recorded interviews were also used. The fine distinctions made in the

to the respondents, unless they asked the enumerator for clarification of a particular point.

Some of the areas for which separate statistics are provided in this report are areas with relatively small numbers of housing units, and the enumeration represents the work of only a few enumerators. Moreover, such items as the delineation of living quarters and the classification of the condition of a housing unit were always determined by the enumerator. To the extent that answers to other census questions were obtained by direct interview, responses may have been affected by misunderstanding on the part of the enumerator. Therefore, misinterpretation of the instructions or variation in interpretation of responses may lead to a wider margin of relative error and response variability in data for small areas (places with relatively small population, or the rural-nonfarm and rural-farm parts of counties) than for large areas. The systematic field review early in the enumeration corrected some of the errors arising from misunderstandings by the enumerator.

In the processing of the data, careful efforts were made at each step to reduce the effects of errors. Errors occurred through failure to obtain complete and consistent information, incorrect recording of information on the FOSDIC schedules or incorrectly transferring it from the self-enumeration forms, faulty markings of the FOSDIC schedules, and the like.

Some of the innovations in the 1960 Census reduced errors and others produced a more consistent quality of results. It is believed that the innovations have improved the quality of the results compared with those of earlier censuses but, at the same time, have introduced an element of difference in the statistics. According to present plans, one or more reports evaluating the statistics of the 1960 Census of Housing will be published later.

Statistics such as the number of owner-occupied and renteroccupied units usually appear in more than one table for a given area. These figures may differ between tables, or in the same table, when characteristics for these units were tabulated at different sample rates (see table A and the section on "Ratio estimation"). In the case of financial characteristics, however, certain types of units were excluded from the tabulations; therefore, differences between the counts obtained from the value and rent distributions and corresponding counts from distributions for other characteristics may reflect the exclusion of these units.

Statistics in this report may differ from those in other reports from the 1960 Census of Housing where different sample rates were used for the same item. Moreover, in some cases, differences caused by errors in enumeration or processing were discovered after the publication of the early reports and were corrected in subsequent reports.

SAMPLE DESIGN AND SAMPLING VARIABILITY

SAMPLE DESIGN

Although some information was collected for all housing units, information for most of the items was collected for samples of housing units. The enumerator was instructed to assign a Sample Key letter (A, B, C, or D) to each housing unit sequentially in the order in which he first visited the unit, whether or not he completed the interview. Each enumerator was given a random key letter to start his assignment, and the order of canvassing was indicated in advance, although the instructions allowed some latitude in the order of visiting individual units at an address. Each housing unit which was assigned the key letter "A" was designated as a sample unit.

Information for housing units in the sample was recorded on a sample FOSDIC schedule. The schedules were bound in books which were so arranged that every fifth sample FOSDIC schedule carried housing questions comprising the 5-percent sample items; the other four-fifths carried questions comprising the 20-percent sample items. Items which appeared on both types of schedules comprised the 25-percent sample items. Thus, sample items were based on 5, 20, or 25 percent of the housing units; for these items the tabulations were based on the full 5-, 20-, or 25-percent sample, respectively. For items enumerated for all housing units, however, the tabulations were not always based on the complete count; data for some of these items were tabulated for a sample of units, particularly for areas with large population. Consequently, the same item may be tabulated at different rates in different tables. The use of different rates was determined largely by the amount of detail to be tabulated.

Sample rate for tabulation.-The rate at which an item was tabulated is given in table A. To illustrate, condition and

for a 25-percent sample for table 12 and from the complete count (100 percent) of units for table 25; value for owneroccupied units was tabulated from the 25-percent sample for each table in which it is presented; and the distribution and median number of persons for all occupied units in table 26 were tabulated from 100-percent count, whereas the medians for owner- and renter-occupied units were tabulated for a 25-percent sample. Data on number of units in structure were tabulated from the 20-percent sample for owneroccupied, renter-occupied, and vacant units. Data on number of rooms for vacant units in table 3 were tabulated from the 100-percent count of vacant units; data on rooms for all units in table 3 were tabulated for a 25-percent sample of occupied and vacant units. Unless otherwise specified, the sample rate for the subject is applicable to the medians and averages as well as the distributions.

Although the sampling procedure did not automatically insure an exact 25-, 20-, or 5-percent sample of housing units in each area, the sample design was unbiased if carried through according to instructions. Biases may have arisen, however, when the enumerator failed to follow the listing and sampling instructions exactly. Generally, for large areas, the deviation from the estimated sample size was found to be quite small. According to preliminary estimates, 24.95 percent of the total housing units in the United States as a whole were designated for the 25-percent sample.

RATIO ESTIMATION

The statistics based on samples of housing units are estimates that were developed through the use of a ratio estimation procedure. Essentially this procedure was carried out for

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STRUCTURAL CHARACTERISTICS

Basement.

Bedrooms,

Rooms:

All units, owner, renter...
Vacant....

Units in structure.

Trailers....

Year structure built.

CONDITION AND PLUMBING
FACILITIES

Bathing facilities..

Bathrooms.....

Condition and plumbing:

All units, owner, renter...

Vacant.....

Sewage disposal.

Source of water.

Toilet facilities.

Water supply...

EQUIPMENT AND FUELS

Air conditioning....

Automobiles available.

Clothes dryer.....

Clothes washing machine.

Cooking fuel....

Heating equipment.

Heating fuel...

Home food freezer.

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For each of the 7 groups, the ratio of the complete count to the sample count of housing units in the group was determined. Each sample housing unit in the group was assigned an integral weight so the sum of the weights would equal the complete count for the group. For example, if the ratio for a group was 4.2, one-fifth of the housing units (selected at random) within the group was assigned a weight of 5, and the remaining four-fifths, a weight of 4. The use of such a combination of integral weights rather than a single fractional weight was adopted to avoid the complications involved in rounding. For the 25-percent sample tabulations, where there were fewer than 50 housing units in the complete count in a group or where the resulting weight was over 16, groups were, in general, combined in a specific order to satisfy these two conditions. Similar procedures with appropriate values were used for the 20- and 5-percent sample tabulations.

The ratio estimates achieve some of the gains of stratifi cation which would have been obtained if the sample had been stratified by the groups for which separate ratio estimates were computed. The net effect is a reduction in the sampling variability and in the bias of many statistics below that which would be obtained by weighting the results of the 25-percent sample by a uniform factor of 4 (the 20-percent sample by 5 or the 5-percent sample by 20). The reduction in sampling variability is trivial for some items and substantial for others.

In tables 1 to 24, 28 to 30, and 35, as a byproduct of the ratio estimation procedure, estimates of owner- and renteroccupied units by color of head of household are essentially in agreement with the total numbers of units from the 100percent counts in the respective groups in each area (occupied units were tabulated for a 25-percent sample and vacant units were tabulated from the 100-percent counts). However, where some of the groups in the ratio estimation procedure were combined, the estimates for owner- and renter-occupied units by color are subject to a relatively small sampling variability. In these tables, the counts of units which are shown under the subject of "Tenure, color, and vacancy status" in the first

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1 Major component of ratio estimate groups; total counts by color and tenure are essentially in agreement with the 100percent counts of units (see section on "Ratio estimation").

2 For owner- and renter-occupied units, median persons and median rooms were computed for a 25-percent sample of units. 3 For automobiles, 20-percent sample in places of 50,000 inhabitants or more in 1950 or in an interim census prior to 1960; 5-percent sample elsewhere. For rent and value of vacant units, 100-percent in places of 50,000 inhabitants or more in 1960 for which statistics are published in 1960 Census of Housing, City Blocks; 25-percent sample elsewhere. For an area including a place of 50,000 inhabitants or more and other territory (e.g., a county, SMSA, or urbanized area), the parts

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table for a given area appear as control totals in subsequent tables for the area. For subjects tabulated from the 20-percent or 5-percent sample, the distributions may not add precisely to these control totals.

In tables 31 and 32 for rural-nonfarm units and tables 33 and 34 for rural-farm units, farm residence was based on a 25-percent sample of units. Estimates of owner- and renteroccupied units by color were inflated to the 100-percent counts for the entire rural portion of the county. The separate counts of rural-nonfarm and rural-farm units, therefore, are subject to some sampling variability.

In tables 25, 26, and 36 to 39, the counts of owner- and renter-occupied units by color and the counts of vacant units, when presented under the subject "Tenure" or "Tenure, color, and vacancy status," are the 100-percent counts, and therefore are not subject to sampling variability. In table 27, the counts of owner-occupied, renter-occupied, and available vacant units also are the 100-percent counts. In tables 40 to 42, all the data are subject to sampling variability.

The ratio estimation procedure was generally applied to the smallest complete geographic area for which data were to be published. Thus, the area may be a city, tract within a city, county, SMSA, urbanized area, or the rural part of a county. The rural-farm and rural-nonfarm parts of a county, however, do not represent complete areas; therefore, distributions of characteristics which were tabulated at different sample rates may not add to the same total. For example, in table 32 for rural-nonfarm units in a county, the total of the distribution of units by number of persons (which was tabulated for a 25percent sample) may differ somewhat from the total of the distribution by home food freezer (which was tabulated from the 5-percent sample).

SAMPLING VARIABILITY

Standard error of numbers and percentages.-The figures from sample tabulations are subject to sampling variability, which can be estimated by using the factors shown in table D in conjunction with table B for absolute numbers and with table C for percentages." These tables do not reflect the effect of response variance, processing variance, or bias arising in the collection, processing and estimation steps. Estimates of the magnitude of some of these factors in the total error are being prepared and will be published at a later date. The chances are about 2 out of 3 that the difference due to sampling variability between an estimate based on a sample and the figure that would have been obtained from a complete count is less than the standard error. The chances are about 19 out of 20 that the difference is less than twice the standard error and about 99 out of 100 that it is less than 2 1/2 times the standard error. The amount by which the estimated standard error must be multiplied to obtain other odds deemed more appropriate can be found in most statistical textbooks.

Table B shows estimates proportionate to the standard errors of estimated numbers of housing units. Table C shows estimates proportionate to the standard errors of estimated percentages of housing units. Table D provides a factor by which the estimates proportionate to the standard errors shown in tables B and C should be multiplied to adjust for the combined effect of the sample design and the estimation procedure.

To estimate a standard error for a given characteristic, locate in table A the sample rate used in the tabulation, and in table D the factor applying to the item according to the sample rate used; multiply this factor by the estimate proportionate

9 These estimates of sampling variability are based on partial information on variances being calculated from a sample of 1960 Census results. More

to the standard error given for the number shown in table B. The product of this multiplication is the approximate standard error. Similarly, to obtain an estimate of the standard error of a percentage, multiply the figure as shown in table C by the factor from table D. For most estimates, linear interpolation in tables B and C will provide reasonably accurate results.

Illustration: Let us assume table 13 shows that in a given city there are an estimated 2,500 housing units with two or more bathrooms. According to table A, data on number of bathrooms in table 13 were tabulated from a 20-percent sample of housing units. Table D shows that when number of bathrooms is tabulated from a 20-percent sample, the appropriate number in table B should be multiplied by a factor of 1.2. Table B shows that the estimate proportionate to the standard error for an estimate of 2,500 is about 80. The factor of 1.2 times 80, or 96, means that the chances are approximately 2 out of 3 that the results of a complete count would not differ by more than 96 from the estimated 2,500. It also follows that there is only about 1 chance in 100 that the results of a complete count would differ by as much as 240, that is, by 2 1/2 times the standard error. Assume also that table 28 shows there are an estimated 300 dilapidated housing units in a given county. According to table A, the sample rate of tabulation for condition and plumbing is 25 percent, and according to table D the factor is 1.2. Table B shows that the estimate proportionate to the standard error for an estimate of 300 is about 32. The factor of 1.2 times 32, or 38, means that the chances are approximately 2 out of 3 that the results of a complete count would not differ by more than 38 from the estimated 300. In table 25, however, the estimated number of dilapidated units was tabulated from the 100-percent count, and, therefore, is not subject to sampling variability.

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