The Bureau is charged with counting every person in the decennial census once, only once, and in the right place. To ensure fairness and consistency in where people are counted, for the first decennial in 1790, Congress established the concept of counting people where they usually reside. The Bureau has relied on that concept ever since. Building on the concept of usual residence, the Bureau subsequently established criteria, which it refers to as residence criteria, to determine where people should be counted during each decennial (see text box). Residence criteria 1. Count people at their usual residence, which is the place where they live and sleep most of the time. 2. People in certain types of group facilities on Census Day are counted at the group facility. 3. People who do not have a usual residence, or who cannot determine a usual residence, are counted where they are on Census Day. For most people, applying the concept of usual residence and the Bureau’s associated residence criteria is straightforward. For others who may be more mobile, like members of the military, college students, migrant farm workers, and people living in group quarters, determining where to count them can be more complicated. Therefore, for each decennial the Bureau issues guidance describing how the criteria should be applied to certain complex living situations for which people commonly request clarification. The guidance is intended to inform the public about how to respond and to assist enumerators and other Bureau staff in administering a proper count. In addition to counting the nation’s population accurately, the Bureau must complete the count and tabulate it against a backdrop of immutable deadlines. The Bureau is required by law to count the population as of April 1, 2020 (Census Day); deliver state apportionment counts to the President by December 31, 2020; and provide redistricting data to the states by April 1, 2021. To meet these deadlines and ensure an accurate count, the Bureau carries out thousands of interrelated activities before, during, and after data collection (see figure 1 for a timeline of selected key activities). The Bureau plans to use its concept of usual residence and its associated residence criteria to determine where to count people in the 2020 Census generally as it did in 2010, but in 2018 the Bureau updated its guidance on how to apply that concept to count people in six complex living situations (see figure 2 for an overview of these changes). In developing the guidance for 2020, the Bureau sought input from external stakeholders on needed changes and solicited public comments on the draft guidance through the Federal Register. In response, the Bureau received input and comments from a variety of entities including federal, state, local, and tribal governments, as well as civil rights and other advocacy organizations. Military and civilian employees of the United States deployed overseas. In 2010, overseas military and civilian employees of the United States who were U.S. citizens were counted at their home state of record for apportionment purposes only. For 2020, the Bureau decided to count these personnel differently depending on whether their permanent duty station was in the United States. Personnel assigned or stationed overseas will continue to be counted as they were in 2010. Personnel stationed in the United States while deployed overseas, however, will instead be counted at their usual home address in the United States for both apportionment and redistricting purposes. According to Bureau documentation, this change resulted from Bureau analysis of data from the Department of Defense which found that personnel deployed overseas were there for shorter periods and were likely to return to their prior usual place of residence, whereas personnel assigned or stationed overseas generally remained overseas for greater periods and often did not return to their prior stateside location. Military and civilian employees of the United States deployed, stationed, or assigned overseas who are legal U.S. residents but not citizens. For 2020, the Bureau plans to count this population the same way it counts U.S. citizens working for the federal government overseas, as described above. According to a Bureau assessment of how it counted personnel overseas in 2010, its guidance for federal agencies that provide the Bureau with data on overseas personnel was unclear on the treatment of non-citizens. According to Bureau officials, it is therefore likely that other federal agencies following that guidance generally excluded non-citizens from the 2010 count. Based on the Bureau’s assessment, the Bureau plans to make clear in its 2020 guidance that U.S.-resident non-citizens working for the federal government overseas are to be counted the same way as U.S. citizens. Bureau officials stated that this change should ensure that U.S.-resident non-citizens are counted more consistently with other U.S. residents. Crews of U.S. maritime and merchant vessels sailing between a U.S. and a foreign port. In 2010, if a U.S. maritime or merchant vessel was sailing between a U.S. and a foreign port on Census Day, then the crewmembers were not counted. For 2020, the Bureau plans to count these crewmembers at their onshore usual residence in the United States or, if they have none, then at the vessel’s U.S. port of departure or arrival. This matches how the Bureau counts crewmembers if their vessel is at a U.S. port or sailing between two U.S. ports. According to Bureau documentation, this change resulted from Bureau analysis and consultation with stakeholders (including the Maritime Administration) which found that crewmembers in each of these situations usually retain an onshore residence in the United States where they live and sleep most of the time so they should be counted in the same way. Juveniles in non-correctional residential treatment centers. For 2020, the Bureau plans to count this population at the U.S. residence where they live and sleep most of the time or, if they have no usual home address, then at the facility. In 2010, they were counted at the facility. The Bureau made this change after concluding that these juveniles typically only stay at residential treatment center facilities temporarily and generally have a usual home elsewhere to which they return after treatment is completed. Religious group quarters residents. For the 2020 Census, the Bureau will count this population at the religious group quarters facility. In 2010, this population was counted at their usual home address or, if they had no usual home address, then at the facility. The Bureau made this change after concluding that this population typically does not have a place of usual residence elsewhere. According to Bureau officials, the Bureau expects the updated guidance will provide greater clarity and result in more informed responses and, thus, higher quality data. Among other things, Bureau officials stated that the data will more accurately reflect the composition of local communities. For the 2020 Census, the Bureau did not change its guidance regarding where to count people in other complex living situations. For example, the Bureau did not make changes to where it will count college students, who will continue to be counted at their parents’ or guardians’ home if they live and sleep there most of the time or, if they live away from their parents’ or guardians’ home, then at their on- or off-campus residence. See table 1 for an overview of where the Bureau will count people in complex living situations the same as it did in 2010. In addition, the Bureau’s guidance includes examples of situations in which people should not be counted in the census, such as the following: people living outside the United States on Census Day who are not military or civilian employees of the U.S. government and are not dependents living with military or civilian employees of the U.S. government; babies born after Census Day or people who die before Census Day; college students living at and attending college outside the United States; and citizens of foreign countries visiting the United States, such as on vacation or a business trip. To help census respondents understand who and where to count household members and others, the Bureau is translating key terms from its census form for 2020 into 59 languages and making it available to community partners and others who may be in a position to help linguistically isolated groups provide accurate responses. It is translating scripted responses to questions about complex living situations into 12 foreign languages to be used by staff who will help answer questions about and take responses over the telephone. The Bureau reports that stakeholder feedback on where to count prisoners largely urged the Bureau to count them at their pre- incarceration addresses to avoid shifting political power to the prison locations at the expense of the prisoners’ home communities. However, the Bureau concluded that counting prisoners anywhere other than the correctional facility would be less consistent with the concept of usual residence, since the majority of people in prisons live and sleep there most of the time. Therefore, for 2020, the Bureau decided that it will continue to count prisoners at the correctional facility as it did in 2010. However, the Bureau will make available to states two tools to allow them to “move” their prisoner population to the prisoners’ pre-incarceration addresses for redistricting purposes. The tools are intended to support such movement within but not across state boundaries. The Bureau is providing states with an online tool that will identify the census geographical block that the population would be tabulated in for any state-provided addresses. If a state wants to “move” the tabulation of specific prisoners within its boundaries, this information will let state officials know which block tabulations to adjust. On November 4, 2019, the Bureau launched the web page that will support states in using this tool. The Bureau plans to update it with 2020 Census geographic data in February 2021, before the Bureau is required to provide redistricting data to the states. The Bureau also plans to provide states with data on group quarters, which will contain a separate count of their prisoner populations, as part of each state’s redistricting file. By including group quarters data in the redistricting file, the Bureau plans to provide these group quarters data to users 1 to 2 months earlier than it did in 2010 when it provided group quarters data separately from the redistricting file. According to the Bureau, this earlier release will benefit many users, including state officials who must consider whether to include or exclude certain populations when redrawing boundaries as a result of state legislation. Once the Bureau has completed its decennial data collection efforts, it generally finds that a small proportion of responses have data quality issues that were not resolved during preceding operations. In these cases, (1) some addresses have multiple responses, (2) some households are missing responses altogether, or (3) some responses include answers that are incomplete or conflict with one another. The Bureau has a variety of plans to resolve these issues (see figure 3). The Bureau may receive multiple census responses from a household for various reasons. For example, different members of the same household could each respond by mail or over the internet, or one member could mail a response and another answer a census worker’s questions in person during the Bureau’s non-response follow-up operation. The Bureau assessed its response processing in 2010, and identified about 14 million responses for households that already had another response (roughly 10 percent of the total number of households included in the final 2010 count). The widespread option to respond over the internet is new for 2020, and while having included it in multiple census tests, Bureau officials have not set expectations on the extent to which it may increase the number of addresses at which it gets multiple responses. To guard against overcounting, as it has in prior decennials, for 2020 the Bureau plans to use an automated routine—referred to as the Primary Selection Algorithm—to determine whom to count at addresses for which it has received multiple responses once data collection is complete. According to Bureau officials, in making this determination, the algorithm takes into account a wide range of information, including results from its fraud detection efforts. We did not examine the algorithm for this review. In addition, to help ensure the integrity of these determinations, the Bureau does not disclose the details of the algorithm publicly and permits only Bureau officials with an operational need to know to access the algorithm. According to Bureau documentation, the Bureau has updated the algorithm for 2020 based on its review of various response scenarios and data from past censuses and census tests. When the Bureau, after its data collection efforts are completed, has been unable to reach anyone able and willing to respond at a particular address or to obtain information about the address and its potential occupants in other ways—such as through neighbors or a building manager—it may be left not knowing whether a housing unit even exists at the address or whether it is occupied, and, if so, by how many people. As it did in 2010, for 2020 the Bureau plans to use a statistical technique it refers to as count imputation to fill in missing data about the existence and number of people living at an address in question. Count imputation has three types. Residence status. This is used when the Bureau does not know whether an address is a real and livable residence. In contrast, it could be a business or in such disrepair that no one could live there. Occupancy status. This is used when the Bureau knows that an address is a real housing unit, but not whether it is vacant or occupied. Household size. This is used when the Bureau knows an address is a real, occupied home, but not how many people live there. To carry out each of these types of count imputation, the Bureau uses a technique referred to as hot-deck imputation which employs continually updated census data from similar nearby households as the basis for filling in the missing statuses and household size. The Bureau has been using some form of hot-deck imputation since at least the 1960 Census. According to Bureau reporting, in 2010, about 500,000 of 137 million addresses counted in the decennial (0.4 percent) were missing an entire response and the Bureau therefore used count imputation to determine a combination of their residence and occupancy status and household size. The Bureau’s count imputation in 2010 added about 1.2 million people to the final census count. For 2020, however, some of the missing responses which otherwise would have required count imputation will instead be resolved through the use of administrative records in conjunction with the Bureau’s door-to-door non-response follow-up effort. Specifically, the Bureau plans to draw on relevant data from records of sufficient quality thereby reducing the amount of follow-up field work needed and the number of households in need of count imputation. According to Bureau officials, they plan to finalize a decision memorandum in December 2019 specifying the Bureau’s thresholds for determining whether administrative records are of sufficient quality for such uses. According to Bureau officials, tests and evaluations performed during the preceding decade demonstrate that these uses of administrative records will provide more accurate results than traditional methods of seeking information about the address from neighbors and others or from count imputation alone. Bureau testing and evaluation also identified improvements to its count imputation technique for 2020, including enhanced use of administrative records in its hot-deck imputation, which it expects will generate results better aligned with actual data for those addresses where it had been missing. Once the Bureau has determined the total number of households and people as of Census Day for apportionment purposes, it resolves incomplete and conflicting information within individual household responses for redistricting and final tabulation purposes. Specifically, for 2020, the Bureau plans to ensure that each household response includes complete and consistent information regarding, for occupied housing units, the age, date of birth, sex, race, and ethnicity (Hispanic or non- Hispanic origin) of each household resident; their relationship to the householder; whether the housing unit is rented or owned by a member of the household; for group quarters, the type of such quarters, such as federal detention center or in-patient hospice facility; and, if the unit is vacant, why (see figure 4). These characteristics (which the Bureau refers to as person and housing characteristics) may be incomplete or conflicting for various reasons, including intentional or accidental omissions or errors by the person filling out the form. According to Bureau data, in 2010, responses for 13 percent of the people counted in the decennial (about 40 million of the about 300 million counted) contained incomplete or conflicting person characteristics that the Bureau had to resolve. For 2020, as it did for 2010, the Bureau plans to use a technique it refers to as edit and characteristic imputation to fill in incomplete and reconcile conflicting information in individual household responses. As summarized in table 2 and described below, it does so using one of three methods, depending on which characteristics are incomplete or conflicting and on what other information the Bureau has about those characteristics. The Bureau has been using some form of characteristic imputation since at least the 1940 Census. Use existing information about same person or household. This method is used when some, but not all, person and household characteristics are incomplete or conflicting and those characteristics can be filled in or reconciled using other information about the same person or household reported within the 2020 response or in prior census or other administrative records. For example, if a person’s date of birth is reported but not his or her age, the Bureau will fill in the age based on the date of birth. If neither age nor date of birth is reported, the Bureau will look to the 2010 Census to fill in both characteristics, adjusting for the intervening years. Use existing information about other people or households. As with the prior method, this method is used when some, but not all, person and household characteristics are incomplete or conflicting. However, unlike the prior method, the incomplete or conflicting characteristics cannot be filled in or reconciled using other information about the same person or household reported within the 2020 response or in prior census or other administrative records. Therefore, the Bureau will look instead to information about other people included in the same 2020 response or to nearby people or households from other 2020 responses. For example, if race is reported for a parent but not a child, the Bureau will fill in the child’s race using the race provided for the parent. If there is no information within the household response that can be used to fill in the child’s race, the Bureau will use a hot-deck imputation method. As discussed earlier, this method employs continually updated census data from similar nearby households as the basis for filling in the needed information. Use existing information about same or other households. This method is used when all person characteristics are incomplete. In this instance, the Bureau will first look to prior census and other administrative records. If the household size reflected in those records matches the household size reflected in the 2020 response, the Bureau will use those records to fill in all person characteristics available in previous census and administrative records. Remaining characteristics not filled in by previous census and other administrative records will be filled in using the methods discussed above. If the household size totals do not match, the Bureau will use a hot-deck imputation method, drawing the missing information from continually updated census data from similar nearby households. As with other areas of the 2020 Census, the key change in the Bureau’s plan for resolving incomplete and conflicting information is the enhanced use of prior census and other administrative records. Specifically, in 2010 the Bureau relied on such records to fill in only race and ethnicity. In contrast, as discussed above, for 2020 the Bureau plans to use prior census and other administrative records as an integral part of its edit and characteristic imputation methods. The Bureau believes this will result in improved data quality and more accurate results. We provided a copy of this draft report to the Department of Commerce. The Census Bureau provided technical comments, which we incorporated as appropriate. We are sending copies of this report to the Secretary of Commerce, the Director of the U.S. Census Bureau, and the appropriate congressional committees. In addition, the report is available at no charge on the GAO website at http://www.gao.gov. If you or your staff have any questions about this report please contact me at (202) 512-2757 or goldenkoff@gao.gov. 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The decennial census produces data vital to the nation. The data are used for congressional apportionment and redistricting; to allocate billions each year in federal funds; and to provide a social, demographic, and economic profile of the nation to guide policy decisions at all levels of government. Given census data's importance, it is incumbent upon the Bureau to ensure their quality. If people are counted in the wrong place, some states and localities may unduly lose or gain political power through apportionment and redistricting disproportionate to their actual population. Poor outcomes can also result if some households are over counted due to multiple responses, not counted due to missing responses, or miscounted due to incomplete or conflicting responses. GAO was asked to describe the Bureau's plans for the 2020 Census to resolve multiple, missing, incomplete, and conflicting responses. This report describes how, for 2020, the Bureau plans to (1) determine where to count people, including those in complex living situations, and how this differs from 2010; and (2) resolve multiple, missing, incomplete, and conflicting responses after data collection, and how this differs from 2010. GAO reviewed relevant Bureau documents and interviewed officials responsible for the 2020 Census. GAO provided a draft of this report to the Bureau. The Bureau provided technical comments, which were incorporated as appropriate. To determine where people should be counted during each decennial census, the Census Bureau (Bureau) has established residence criteria (see figure). For most people, applying these criteria is straightforward. For others who may be more mobile, like members of the military, college students, migrant farm workers, and people living in group quarters such as federal detention centers or in-patient hospice facilities, it can be more complicated. Therefore, for each decennial the Bureau issues guidance describing how the criteria should be applied to certain complex living situations. For the 2020 Census, the Bureau has updated its guidance on where to count people in six complex living situations, such as U.S. employees deployed overseas. The Bureau plans to count people in other living situations in the same manner as it did in 2010. As in 2010, the Bureau will count prisoners at the correctional facility where they are housed, but also plans to make other resources available to states that want to use prisoners' in-state, pre-incarceration addresses for redistricting purposes instead of their prison addresses. To resolve multiple responses for a single address, for 2020 the Bureau plans to use a longstanding automated routine—its Primary Selection Algorithm—to determine who to count at the address. For 2020, Bureau documents indicate it updated the algorithm after reviewing various response scenarios and data from past censuses and tests. To resolve missing household responses following data collection, as it did in 2010, the Bureau plans to use for 2020 a technique it refers to as count imputation, which draws data from similar nearby households to determine whether a housing unit exists, whether it is occupied, and, if so, by how many people. However, for 2020, the Bureau will also try to reduce the number of households which otherwise would have required count imputation and help reduce follow-up field work by drawing on relevant data from administrative records of sufficient quality in conjunction with its non-response follow-up field work. To resolve incomplete and conflicting information within a household response, the Bureau plans to use a technique it refers to as edit and characteristic imputation. This technique involves drawing data from the same household response, prior census and other administrative records or similar nearby households, which the Bureau believes will improve data quality and produce more accurate results.