This report provides an overview of selected issues regarding census data that have arisen during recent decennial censuses, including use of sampling or other estimation techniques and counting U.S. citizens residing abroad. The Constitution requires that members of the House of Representatives "shall be apportioned among the several States according to their respective numbers, counting the whole numbers of persons in each State, excluding Indians not taxed," and to this end an "actual Enumeration shall be made ... within every subsequent Term of ten Years, in such manner as [Congress] shall by Law direct." The framers of the Constitution provided for a simple population headcount and made no provision for counts by sex, age, or address. The census was to provide figures to adjust periodically apportionment of representatives among the states. It was also originally intended to provide figures for determining proportionate shares of direct taxes for states. Congress has established and authorized the U.S. Census Bureau, an agency within the Department of Commerce, to administer the decennial population census and other surveys. In addition to determining the apportionment of Representatives among the states, decennial population census data fulfills several purposes: provides state and local governments a basis for establishing district boundaries for congressional, state legislative, and local representative bodies, because the data is generally considered to be the best available, although its use is not expressly mandated; determines allocation of electoral votes among states for presidential elections; determines allocations and/or triggers federal and state funding for a variety of public benefits and assistance programs; and triggers certain voting rights, such as identifying when the 10,000 single-language-minority citizens of voting age threshold is reached for the bilingual balloting provisions of the Voting Rights Act of 1965. With regard to intrastate redistricting, all 50 states, the District of Columbia, and Puerto Rico currently receive census data for reapportionment and redistricting via the P.L. 94-171 census program. Under this program, the Census Bureau provides states decennial census figures for state-identified geographic areas and election precincts to use for intrastate redistricting activities prior to April 1 of the year following the decennial census. In addition, the President transmits figures for House of Representatives apportionment to Congress and each state by the end of the first week of the regular congressional session following the decennial census. The Constitution requires Congress to use census data to apportion Representatives among the states but does not expressly require states to use census data for intrastate congressional and state legislative redistricting. Courts, however, have held that states must use the best data available, regardless of whether it is census apportionment data. Federal court findings that states are not required to use federal census data for redistricting but must use the best data available has raised questions over whether the Census Bureau must provide states with adjusted census data in addition to census apportionment data. Courts have generally found that the Census Bureau is not required to provide such adjusted data The best available data principle was set forth in the 1969 Supreme Court decision Kirkpatrick v. Preisler . In this case, the Supreme Court invalidated Missouri's congressional redistricting plan but indicated that Missouri's use of projected population figures was not per se invalid if such data would have a higher degree of accuracy than other available data. However, the Kirkpatrick Court stated that, in the instant case, the federal decennial census data were the best data available. In Senate of the State of California v. Mosbacher , the Ninth Circuit addressed whether the Census Bureau was required to provide states adjusted census data for state intrastate redistricting activities. In California, the California state senate sued the Secretary of Commerce to release adjusted data after the Census Bureau decided not to adjust the official 1990 census data. In reaching its decision, the Ninth Circuit noted that if a state knows that census data is underrepresentative of the population, it can and should utilize non-census data, in addition to the official count, for redistricting. The Ninth Circuit found, however, that the Secretary of Commerce had no affirmative duty under the Census Clause of the Federal Constitution (Art. 1, §2, cl. 3) or federal law to provide states adjusted census data. Similarly, in City of Los A ngeles v. U.S. Dep't. of Commerce , the Ninth Circuit held that the Secretary of Commerce had no obligation under 13 U.S.C. §195 to adjust the official 2000 decennial census figures for intrastate redistricting purposes. The circuits are divided on whether adjusted census data must be released under the Freedom of Information Act. In Assembly of the State of California v. U.S. Department of Commerce , the same court affirmed a lower court's decision requiring the Department of Commerce to release computer tapes containing statistically adjusted data from the 1990 census to the Assembly under the Freedom of Information Act, noting that "states are not obliged to use official census data when drawing their state legislative or congressional districts." However, Florida House of Representatives v. U.S. Department of Commerce , the U.S. Court of Appeals for the Eleventh Circuit held that the statistically adjusted data was exempt from disclosure under the Freedom of Information Act. While states may use non-apportionment census data for redistricting purposes, such adjusted data must be able to withstand scrutiny. For example, in Young v. Klutznick , the city of Detroit sued the Department of Commerce regarding an adjustment to an alleged undercount in the 1980 census data. In dicta, the Sixth Circuit stated that the state legislature is not required by the federal Constitution to use Census Bureau data for congressional redistricting, but could use adjusted population figures when redistricting between decennial censuses, as long as any adjustment is thoroughly documented and applied systematically. Similarly, in City of Detroit v. Franklin , the city sought to adjust an alleged undercount in the 1990 census data, arguing that Young had been overruled by Karcher v. Daggett . The city argued that in Karcher the U.S. Supreme Court had held that the apportionment clause imposes an obligation on states to use only the official population count as determined by the Census Bureau in redistricting. This argument was probably based on the sentence in Karcher that "[a]dopting any standard other than population equality, using the best census data available ... would subtly erode the Constitution's ideal of equal representation" and the fact that the Karcher Court considered the census data the only reliable indication of the districts' relative population levels. In City of Detroit , the District Court held, however, that the plaintiffs misconstrued Karcher and that it did not require states to use census figures in redistricting or overrule Young . Rather, the Supreme Court had "merely reiterated a well-established rule of constitutional law: states are required to use the 'best census data available' or 'the best population data available' in their attempts to effect proportionate political representation." Federal courts have also examined whether state legislatures are required to use total population data for redistricting activities. In these cases, courts have found that the best available data standard does not necessarily require use of total population figures. For example, in Burns v. Richardson , the Supreme Court held that in state legislative redistricting cases the Constitution "does not require the states to use total population figures derived from the federal census as the standard" of measurement. The Court noted that in earlier cases it had been careful to leave open the question of the appropriate population basis for redistricting activities, even though total population figures were, in fact, the basis for determining whether the Equal Protection Clause of the Constitution had been violated in several cases. In Burns , Hawaii had used the number of registered voters as the basis for redistricting the state senate. The Court found that the redistricting plan "satisfies the Equal Protection Clause only because on this record it was found to have produced a distribution of legislators not substantially different from that which would have resulted from the use of a permissible population basis." Hawaii was found to have a unique situation, wherein significant numbers of tourists, military personnel, and other transient population segments distorted the distribution of actual state citizens. The redistricting plan that would have resulted from using the total population would not have reflected the true state population distribution as accurately as one based on state citizenship. Since a registered voter population basis was the closest approximation of the state citizen population, use of the registered voter population was deemed consistent with the Equal Protection Clause. However, the Court was careful to note that Burns did not establish the validity of its unique redistricting population basis for all time or circumstances. Although federal decennial census figures need not be used as the basis for redistricting, any alternate data must be shown to be the best available or justified by particular circumstances that will result in a more accurate redistricting plan than one based on total population figures from the federal decennial census. The Supreme Court has not addressed the constitutionality or propriety of using total population as opposed to voting population for intrastate redistricting when use of total population would produce a disparity in voter strength between districts with equal total populations. In Garza v. County of Los Angeles , the County of Los Angeles disputed a court-ordered redistricting plan that used total population. The U.S. Court of Appeals for the Ninth Circuit rejected the County's arguments to hold that redistricting based on voting populations instead of the total population would be unconstitutional. Justice Thomas, however, in his dissent from a denial of a writ of certiorari in Chen v. City of Houston , contrasted the Ninth Circuit decision in Garza with Fourth and Fifth Circuit decisions holding that whether to use total population as opposed to voting population for redistricting within a state should be determined through the legislative and political process. Although most states prescribe state legislative redistricting procedures through statute, many do not have a statutory procedure for congressional redistricting. In such states, state legislatures conduct congressional redistricting on an ad hoc basis after a federal decennial census.