A key measure of the success of a data collection effort is the final response rate. The American Community Survey (ACS) achieves a high total response rate each year, due in part to the data collection design, which in turn reflects the experience and research in data collection strategies drawn from the U.S. Census Bureau's decennial census and demographic survey programs. Success, however, would not be possible without the high quality of the actual data collection, which is due to the efforts of the interviewing staff in the telephone centers and regional offices. This success also is related to the mandatory nature of the survey. Title 13 of the United States Code [U.S.C.] authorizes the Census Bureau to conduct the ACS, requires households to participate, and requires the Census Bureau to keep confidential all information collected.

The data collection operation for housing units (HUs) consists of three modes: mail, telephone, and personal visit. For most HUs, the first phase includes a questionnaire mailed to the sample address, with a request to the household to complete the questionnaire and return it by mail. If no response is received, the Census Bureau follows up with computer-assisted telephone interviewing (CATI) when a telephone number is available. If the Census Bureau is unable to reach an occupant using CATI, or if the household refuses to participate, the address may be selected for computer-assisted personal interviewing (CAPI).

Figure 7.1 ACS Data Collection Consists of Three Overlapping Phases

ACS sample panel	Month of data collection
	2005		2006
	November	December	January	February	March	April	May	June
November 2005	Mail	Phone	Personal visit
December 2005		Mail	Phone	Personal visit
January 2006			Mail	Phone	Personal visit
February 2006				Mail	Phone	Personal visit
March 2006					Mail	Phone	Personal visit
April 2006						Mail	Phone	Personal visit
May 2006						Mail	Phone
June 2006							Mail

The ACS includes 12 monthly independent samples. Data collection for each sample lasts for 3 months, with mail returns accepted during this entire period, as shown in Figure 7.1. This three phase process operates in continuously overlapping cycles so that, during any given month, three samples are in the mail phase, one is in the CATI phase, and one is in the CAPI phase.

Figure 7.2 summarizes the distribution of interviews and noninterviews for the 2007 ACS. Among the ACS sample addresses eligible for interviewing in the United States, approximately 47 percent were interviewed by mail, 10 percent by CATI, and 41 percent were represented by CAPI interviews. Two percent were noninterviews.

Figure 7.2 Distribution of ACS Interviews and Noninterviews

Mail is the least expensive method of data collection, and the success of the program depends on high levels of mail response. Sample addresses are reviewed to determine whether the available information is sufficient for mailing. The requirement for a "mailable" address in the United States is met if there is either a complete city-style or rural route address. A complete city-style address includes a house number, street name, and ZIP Code. (The town or city and state fields are not required because they can be derived from the ZIP Code.) A complete rural-route address includes a rural-route number, box number, and ZIP Code. About 95 percent of the 2007 sample addresses in the United States met these criteria and were designated as mailable.

The requirement for a mailable address differs slightly in Puerto Rico. In addition to the criteria for the United States, sample city-style addresses in Puerto Rico also must have an "urbanización" name, building name, or condominium name to be considered mailable. About 72 percent of the addresses in Puerto Rico were considered mailable in 2007.

Examples of unmailable addresses include those with only physical descriptions of an HU and its location, or with post office (P.O.) box addresses, as well as addresses missing place names and ZIP Codes. P.O. box addresses are considered unmailable because of the unknown location of the HU using the P.O. box. Addresses missing ZIP Codes are considered unmailable when the place name is also missing. HU addresses not meeting one of the completeness criteria are still included in the sample frame, but they bypass the mail and telephone phases.

The second data collection phase is the telephone phase, or CATI. The automated data collection instrument (the set of questions, the list of response categories, and the logic that presents the next appropriate question based on the response to a given question) is written in BLAISE, an open-source scripting software language. The CATI instrument is available in English and Spanish in both the United States and Puerto Rico.

To be eligible for CATI, an HU that did not respond by mail must have a mailable address and a telephone number. The Census Bureau contracts with vendors who attempt to match the ACS sample addresses to their databases of addresses and then provide telephone numbers. There are two vendors for United States addresses and one for Puerto Rico addresses and, since the vendors use different methodologies and sources, one may be able to provide a telephone number while another may not. This matching operation occurs each month before a sample is mailed. About a month later, just prior to the monthly CATI work, headquarters staff transmit a file of the CATIeligible sample addresses and telephone numbers to a common queue for all three telephone call centers.

The Census Bureau conducts CATI from its three telephone call centers located in Jeffersonville, Indiana; Hagerstown, Maryland; and Tucson, Arizona. The CATI operation begins about 5 weeks after the first mail package is sent out. A control system, WebCATI, is used to assign the cases to individual telephone interviewers. As CATI interviewers begin contacting the households, the Web- CATI system evaluates the skills needed for each case (for example, language or refusal conversion skills) and delivers the case to those interviewers who possess the requisite skill(s).

Once a CATI interviewer reaches a person, the first task is to verify that the interviewer has contacted the correct address. If so, the interviewer attempts to complete the interview. If the householder refuses to participate in the CATI interview, a different CATI interviewer trained in dealing with refusals will call the household after a few days. If the household again refuses, CATI contact attempts are stopped, and the case is coded as a noninterview. If a households questionnaire is received at any time during the CATI operation, that case is removed from the CATI sample and is considered a mail response. Each day, NPC staff transmit a file with the status of each case, and headquarters staff update the status on the control file.

The CATI operation has a strong quality assurance program, including CATI software-related quality assurance and monitoring of telephone interviewers. The CATI instrument has a sophisticated, integrated set of checks to prevent common errors. For example, a telephone interviewer cannot input out-of-range responses, skip questions that should have been asked, or ask questions that should have been skipped. Both new and experienced telephone interviewers are subject to random monitoring by supervisors to ensure that they follow procedures for asking questions and effectively probe for answers, and to verify that the answers they enter match the answers provided by the respondent.

Approximately 650 interviewers conduct CATI interviews from the Census Bureau's three telephone call centers. Interviewers participate in a 3-day classroom training session to learn and practice the appropriate interviewing procedures. They have 25 to 26 calendar days to complete the monthly CATI caseload, which averaged in 2006 and 2007 about 95,000 cases each month. At the end of the CATI interview cycle, all cases receive a CATI outcome code in one of three general categories: interview, noninterview, or ineligible for CATI. This last category includes cases with incorrect telephone numbers. Cases in the last two categories are eligible for the personal visit phase.

The last phase of ACS data collection is the personal visit phase, or CAPI. This phase usually begins on the first day of the third month of data collection for each sample, and typically lasts for the entire month.

After mail and CATI operations have been completed, a CAPI subsample is selected from two categories of cases. Mailable addresses with neither a response to the mailout nor a telephone interview are sampled at a rate of 1 in 2, 2 in 5, or 1 in 3 based on the expected rate of completed interviews at the tract level. Unmailable addresses are sampled at a rate of 2 in 3 (U.S Census Bureau 2007).

The CAPI operation is conducted by Census Bureau field representatives (FR's) operating from the Census Bureau's 12 regional offices (ROs). The sampled cases are distributed among the 12 ROs based on their geographic boundaries. The Boston RO is responsible for CAPI data collection in Puerto Rico.

After the databases containing the sample addresses are distributed to the appropriate RO, the addresses are assigned to FR's. FR's can conduct interviews by telephone or personal visit, using laptop PCs loaded with a survey instrument similar to the one used in the CATI operation. The CAPI instrument is available in English and Spanish in the United States and Puerto Rico.

If a telephone number is available, the FR will first attempt to call the sample address. There are two exceptions: (1) unmailable addresses, because an FR would not be able to verify the location of the address over the telephone; and (2) refusals from the CATI phase, because these residents already have refused a telephone interview. The FR will call and confirm that he or she has reached the sample address. If so, the FR uses the automated instrument and attempts to conduct the interview. If an FR cannot reach a resident after calling three to five times at different times of the day during the first few days of the interview period, he or she must make a personal visit.

Approximately 80 percent of CAPI cases require an FR visit. In addition to trying to obtain an interview, a visit is needed to determine whether the HU exists and to determine the occupancy status. If an HU does not exist at the sample address, that status is documented. If an FR verifies that an HU is vacant, he or she will interview a knowledgeable respondent, such as the owner, building manager, real estate agent, or a neighbor, and conduct a "vacant interview" to obtain some basic information about the HU. If the HU is currently occupied, the FR will conduct an occupied or "temporarily occupied" interview. An FR conducts a temporarily occupied interview when there are residents living in the HU at the time of the FR's visit, but no resident has been living there or plans to live there for more than 2 months.

The FR's are trained to remain polite but persistent when attempting to obtain responses. They also are trained in how to handle almost any situation, from responding to a household that claims to have returned its questionnaire by mail to conducting an interview with a non-English speaking respondent.

When FR's cannot obtain interviews, they must indicate the reason. Such noninterviews are taken seriously, because they have an impact on both sampling and nonsampling error. Noninterviews occur when an eligible respondent cannot be located, is unavailable, or is unwilling to provide the survey information. Additional noninterviews occur when FR's are unable to confirm the status of a sample HU due to restricted access to an area because of a natural disaster or nonadmission to a gated community during the interview period. Some sample cases will be determined to be ineligible for the survey. These include sample addresses of structures under construction, demolished structures, and nonexistent addresses.

One of the tasks for an FR is to check the geographic codes (state, county, tract, and block) for each address he or she visits. The FR either confirms that the codes are correct, corrects them, or records the codes if they are missing.

Approximately 3,500 FR's conduct CAPI interviews across the United States and Puerto Rico. Interviewers have almost the entire month to complete the monthly CAPI caseload, which averages more than 40,000 cases each month. Each day, FR's transmit a file with the status of all personal visit cases, and headquarters staff update the statuses on the control file.

FR's participate in a 4-day classroom training session to learn and practice the appropriate interviewing procedures. Supervisors travel with FR's during their first few work assignments to observe and reinforce the procedures learned in training. In addition, a sample of FR's is selected each month and supervisors reinterview a sample of their cases. The primary purpose of the reinterview program is to verify that FR's are conducting interviews, and doing so correctly.

Remote areas of Alaska provide special difficulties when interviewing, such as climate, travel, and seasonality of the population. To address some of these challenges, the Census Bureau has designated some of these areas to use different procedures for ACS interviewing.

For areas of Alaska that the Census Bureau defines as remote, ACS operations are different from those operations in the rest of the country. The Census Bureau does not mail questionnaires to Remote Alaska sample units and Remote Alaska respondents do not complete any interviews on a paper questionnaire. We do not attempt to conduct interviews with households in Remote Alaska via Census Bureau telephone center interviewers. All interviews for Remote Alaska are conducted using personal visit procedures only.

In order to allow FR's in Alaska adequate time to resolve some of the transportation and logistical challenges associated with conducting interviews in Remote Alaska areas, the normal period for interviewing is extended from 1 month to 4 months. There are two 4-month interview periods every year in Remote Alaska. The first starts in January and stops at the end of April. The second starts in September and stops at the end of December. These months were identified as most effective in allowing FR's to gain access to remote areas, and in finding residents of Native Villages at home who might be away during the remaining months participating in subsistence activities. For some boroughs designated as partially remote by the Census Bureau, hub cities in these boroughs are not included in these Remote Alaska procedures. These cities would have cases selected for sample each month of the year, and would be eligible to receive a mail questionnaire, or to be contacted by a telephone center or personal visit interviewer. Table 7.1 provides a list of Remote Alaska areas and their associated interview periods.

Table 7.1 Remote Alaska Areas and Their Interview Periods

Borough name	All or part of borough designated remote	Interview period for the remote portion of the borough
		January-April	September-December
Aleutians East	All	(X)
Aleutian Islands	All		(X)
Bethel	Part	½	½
Bristol Bay	All	(X)
Denali	All		(X)
Dillingham	Part	(X)
Lake and Peninsula	All		(X)
Nome	Part	½	½
North Slope	Part	(X)
Northwest Arctic	All	½	½
Southeast	All	½	½
Valdez-Cordova	Part	½	½
Wade Hampton	All	½	½
Yukon-Koyukuk	All	½	½

Note: An X indicates that all workload falls in the interview period.

U.S. Census Bureau. 2007. "Accuracy of the Data (2006)." Washington, DC, 2005 .