Aggregate gross rent is calculated by adding together all the gross rents for all specified housing units in an area. Aggregate gross rent is rounded to the nearest hundred dollars. (For more information, see Aggregate under "Derived Measures.")

Many processing procedures are necessary to prepare the ACS data for tabulation. In this section, we examine each data preparation procedure separately. These procedures occur daily or monthly, depending on the file type (control or data capture) and the data collection mode (mail, CATI, or CAPI). The processing that produces the final input files for data products is conducted on a yearly basis.

The HU data are collected on a continual basis throughout the year by mail, CATI, and CAPI. Sampled households first are mailed the ACS questionnaire; those households for which a phone number is available that do not respond by mail receive telephone follow-up. As discussed in Chapter 7, a sample of the noncompleted CATI cases is sent to the field for in-person CAPI interviews, together with a sample of cases that could not be mailed. Each day, the status of each sample case is updated in the ACS control file based on data from data collection and capture operations. While the control file does not record response data, it does indicate when cases are completed so as to avoid additional attempts being made for completion in another mode.

The creation and processing of the data depends on the mode of data collection. Figure 10.2 shows the monthly processing of HU response data. Data from questionnaires received by mail are processed daily and are added to a Data Capture File (DCF) on a monthly basis. Data received by mail are run through a computerized process that checks for sufficient responses and for large households that require follow-up. Cases failing the process are sent to the FEFU operation. As discussed in more detail in Chapter 7, the mail version of the ACS asks for detailed information on up to five household members. If there are more than five members in the household, the FEFU process also will ask questions about those additional household members. Telephone interviewers call the cases with missing or inconsistent data for corrections or additional information. The FEFU data are also included in the data capture file as mail responses. The Telephone Questionnaire Assistance (TQA) operation uses the CATI instrument to collect data. These data are also treated as mail responses, as shown in Figure 10.2.

Figure 10.2 Daily Processing of Housing Unit Data



CATI follow-up is conducted at three telephone call centers. Data collected through telephone interviews are entered into a BLAISE instrument. Operational data are transmitted to the Census Bureau headquarters daily to update the control file with the current status of each case. For data collected via the CAPI mode, Census Bureau field representatives (FR's) enter the ACS data directly into a laptop during a personal visit to the sample address. The FR transmits completed cases from the laptop to headquarters using an encrypted Internet connection. The control file also is updated with the current status of the case. Each day, status information for GQs is transmitted to headquarters for use in updating the control file. The GQ data are collected on paper forms that are sent to the National Processing Center on a flow basis for data capture.

This measure divides the gross rent as a percentage of household income distribution into two equal parts: one-half of the cases falling below the median gross rent as a percentage of household income and one-half above the median. Median gross rent as a percentage of household income is computed on the basis of a standard distribution. (See the "Standard Distributions" section under "Derived Measures.") Median gross rent as a percentage of household income is rounded to the nearest tenth. (For more information on medians, see "Derived Measures.")

The ACS questionnaire includes a set of questions that offer the possibility of write-in responses, each of which requires coding to make it machine-readable. Part of the preparation of newly received data for entry into the DCF involves identifying these write-in responses and placing them in a series of files that serve as input to the coding operations. The DCF monthly files include HU and GQ data files, as well as a separate file for each write-in entry. The HU and GQ write-ins are stored together. Figure 10.4 diagrams the general ACS coding process.

Figure 10.4 American Community Survey Coding



During the coding phase for write-in responses, fields with write-in values are translated into a prescribed list of valid codes. The write-ins are organized into three types of coding: backcoding, industry and occupation coding, and geocoding. All three types of ACS coding are automated (i.e., use a series of computer programs to assign codes), clerically coded (coded by hand), or some combination of the two. The items that are sent to coding, along with the type and method of coding, are illustrated below in Table 10.1.

Table 10.1 ACS Coding Items, Types, and Methods

Item	Type of coding	Method of coding
Race	Backcoding	Automated with clerical follow-up
Hispanic origin	Backcoding	Automated with clerical follow-up
Ancestry	Backcoding	Automated with clerical follow-up
Language	Backcoding	Automated with clerical follow-up
Industry	Industry	Clerical
Occupation	Occupation	Clerical
Place of birth	Geocoding	Automated with clerical follow-up
Migration	Geocoding	Automated with clerical follow-up
Place of work	Geocoding	Automated with clerical follow-up

For the 1996-1998 American Community Survey, the question, which was asked of persons 5 years old and over, instructed the respondents to mark each appropriate box if they had difficulty with any of the following three specific functions: "Difficulty seeing (even with glasses)," "Difficulty hearing (even with a hearing aid)," or "Difficulty walking." The respondents could mark as many as three boxes depending on their functional limitation status. If the respondents did not have difficulty with any of the three specific functions, the question instructed them to mark the box labeled "None of the above." The sensory and physical disability data obtained from the 1996-1998 American Community Survey are not comparable to data collected from the 1999-2006 American Community Surveys.

The first type of coding is the one involving the most items-backcoding. Backcoded items are those that allow for respondents to write in some response other than the categories listed. Although respondents are instructed to mark one or more of the 12 given race categories on the ACS form, they also are given the option to check "Some Other Race," and to provide write-in responses. For example, respondents are instructed that if they answer "American Indian or Alaska Native," they should print the name of their enrolled or principal tribe; this allows for a more specific race response. Figure 10.5 illustrates backcoding.

All backcoded items go through an automated process for the first pass of coding. The written-in responses are keyed into digital data and then matched to a data dictionary. The data dictionary contains a list of the most common responses, with a code attached to each. The coding program attempts to match the keyed response to an entry in the dictionary to assign a code. For example, the question of language spoken in the home is automatically coded to one of 380 language categories. These categories were developed from a master code list of 55,000 language names and variations. If the respondent lists more than one non-English language, only the first language is coded.

However, not all cases can be assigned a code using the automated coding program. Responses with misspellings, alternate spellings, or entries that do not match the data dictionary must be sent to clerical coding. Trained human coders will look at each case and assign a code. One example of a combination of autocoding and follow-up clerical coding is the ancestry item. The write-in string for ancestry is matched against a census file containing all of the responses ever given that have been associated with codes. If there is no match, an item is coded manually. The clerical coder looks at the partial code assigned by the automatic coding program and attempts to assign a full code.

To ensure that coding is accurate, 10 percent of the backcoded items are sent through the quality assurance (QA) process. Batches of 1,000 randomly selected cases are sent to two QA coders who independently assign codes. If the codes they assign do not match one another, or the codes assigned by the automated coding program or clerical coder do not match, the case is sent to adjudication. Adjudicator coders are coding supervisors with additional training and resources. The adjudicating coder decides the proper code, and the case is considered complete.

Figure 10.5 Backcoding

This category includes gas piped through underground pipes from a central system to serve the neighborhood.

This category includes liquid propane gas stored in bottles or tanks that are refilled or exchanged when empty.

Electricity is generally supplied by means of above or underground electric power lines.

Each HU is assigned a response type that describes its status as occupied, temporarily occupied, vacant, a delete, or noninterview. Deleted HUs are units that are determined to be nonexistent, demolished, or commercial units, i.e., out of scope for ACS.

While this type of classification already exists in the DCF, it can be changed from "occupied" to "vacant" or even to "noninterview" under certain circumstances, depending on the final number of persons in the HU, in combination with other variables. In general, if the return indicates that the HU is not occupied and that there are no people listed with data, the record and number of people (which equals 0) is left as is. If the HU is listed as occupied, but the number of persons for whom data are reported is 0, it is considered vacant.

The data also are examined to determine the total number of people living in the HU, which is not always a straightforward process. For example, on a mail return, the count of people on the cover of the form sometimes may not match the number of people reported inside. Another inconsistency would be when more than five members are listed for the HU, and the FEFU fails to get information for any additional members beyond the fifth. In this case, there will be a difference between the number of person records and the number of people listed in the HU. To reconcile the numbers, several steps are taken, but in general, the largest number listed is used. (For more details on the process, see Powers [2006].)

The acceptability index is a data quality measure used to determine if the data collected from an occupied HU or a GQ are complete enough to include a person record. Figure 10.13 illustrates the acceptability index. Six basic demographic questions plus marital status are examined for answers. One point is given for each question answered for a total of seven possible points that could be assigned to each person in the household. A person with a response to either age or date of birth scores two points because given one, the other can be derived or assigned. The total number of points is then divided by the total number of household members. For the interview to be accepted, there must be an average of 2.5 responses per person in the household. Household records that do not meet this acceptability index are classified as noninterviews and will not be included in further data processing. These cases will be accounted for in the weighting process, as outlined in Chapter 11.

Figure 10.13 Acceptability Index

Once the universe of acceptable interviews is determined, the HU data are reviewed to unduplicate multiple returns for a single HU. There are several reasons why more than one response can exist for an HU. A household might return two mail forms, one in response to the initial mailing and a second in response to the replacement mailing. A household might return a mailed form, but also be interviewed in CATI or CAPI before the mail form is logged in as returned. If more than one return exists for an HU, a quality index is used to select one as the final return. This index is calculated as the percentage of items with responses out of the total number of items that should have been completed. The index considers responses to both population and housing items. The mode of each return also is considered in the decision regarding which of two returns to accept, with preference generally given to mail returns. If two mail returns are received, preference generally is given to the earliest return. For the more complete set of rules, see Powers (2006).

After the resolution of multiple returns, each sample case is assigned a value for three critical variables-data collection mode, month of interview, and case status. The month in which data were collected from each sample case is determined and then used to define the universe of cases to be used in the production of survey estimates. For example, data collected in January 2007 were included in the 2007 ACS data products, even if the returns were sampled in 2006, while ACS surveys sent out in November 2007 were included in the 2007 ACS data products if they were received by mail or otherwise completed by December 31, 2007. Surveys sent out in November 2007 that were received by mail or otherwise completed after December 31, 2007, will be included in the 2008 ACS data products.

This category includes heat provided by sunlight that is collected, stored, and actively distributed to most of the rooms.

Select Files are the series of files that pertain to those cases that will be included in the Edit Input File. As noted above, these files include the case status, the interview month, and the data collection mode for all cases. The largest select file, also called the Omnibus Select File, contains every available case from 14 months of sample-the current (selected) year and November and December of the previous year. This file includes acceptable and unacceptable returns. Unacceptable returns include initial sample cases that were subsampled out at the CAPI stage,² returns that were too incomplete to meet the acceptability requirements. In addition, while the "current year" includes all cases sampled in that year, not all returns from the sampled year were completed in that year. This file is then reduced to include only occupied housing units and vacant units that are to be tabulated in the current year. That is, returns that were tabulated in the prior year, or will be tabulated in the next year, are excluded. The final screening removes returns from vacant boats because they are not included in the ACS estimation universe.

Footnote:

²See Chapter 7 for a full discussion of subsampling and the ACS.

The next step is the creation of the Housing Edit Input File and the Person Edit Input File. The Housing Edit Input file is created by first merging the Final Accepted Select File with the DCF housing data. Date variables then are modified into the proper format. Next, variables are given the prefix "U," followed by the variable name to indicate they are unedited variables. Finally, answers that are "Don't Know" and "Refuse" are set as missing blank values for the edit process.

The Person Edit Input File is created by first merging the DCF person data with the codes for Hispanic origin, race, ancestry, language, place of work, and current or most recent job activity. This file then is merged with the Final Accepted Select File to create a file with all person information for all accepted HUs. As was done for the housing items, the person items are set with a "U" in front of the variable name to indicate that they are unedited variables. Next, various name flags are set to identify people with Spanish surnames and those with "non-name" first names, such as "female" or "boy." When the adjudicated number of people in an HU is greater than the number of person records, blank person records are created for them. The data for these records will be filled in during the imputation process. Finally, as with the housing variables, "Don't Know" and "Refuse" answers are set as missing blank values for the edit process. When complete, the Edit Input Files encompass the information from the DCF housing and person files but only for the unduplicated response records with data collected during the calendar year.

Since 1996, the American Community Survey questions have remained the same.

The data on year householder moved into unit were obtained from answers to Housing Question 3, which was asked at occupied housing units. These data refer to the year of the latest move by the householder. If the householder moved back into a housing unit he or she previously occupied, the year of the latest move was reported. If the householder moved from one apartment to another within the same building, the year the householder moved into the present apartment was reported. The intent is to establish the year the present occupancy by the householder began. The year that the householder moved in is not necessarily the same year other members of the household moved in, although in the great majority of cases an entire household moves at the same time.

Median year householder moved into unit divides the distribution into two equal parts: one-half of the cases falling below the median year householder moved into unit and one-half above the median. Median year householder moved into unit is computed on the basis of a standard distribution. (See the "Standard Distributions" section under "Derived Measures.") Median year householder moved into unit is rounded to the nearest calendar year. (For more information on medians, see "Derived Measures.")

Since 1996, the question provided two write-in spaces for the respondent to enter month and year the householder (person 1) moved into the house, apartment, or mobile home.