The Constitutions Census Clause authorizes Congress to direct an "actual Enumeration" of the American public every 10 years to provide a basis for apportioning congressional representation among the States. Pursuant to this authority, Congress has enacted the Census Act (Act), 13 U. S. C. §1 et seq., delegating the authority to conduct the decennial census to the Secretary of Commerce (Secretary). The Census Bureau (Bureau), which is part of the Department of Commerce, announced a plan to use two forms of statistical sampling in the 2000 Decennial Census to address a chronic and apparently growing problem of "undercounting" of some identifiable groups, including certain minorities, children, and renters. In early 1998, two sets of plaintiffs filed separate suits challenging the legality and constitutionality of the plan. The suit in No. 98-564 was filed in the District Court for the Eastern District of Virginia by four counties and residents of 13 States. The suit in No. 98-404 was f