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A “First‐Cut” at Forming Rural PSUs

Susan L. King


After every decennial census, many surveys including the Consumer Expenditure Survey (CE) redefine their primary sampling units (PSUs), which are small sets of adjacent counties. CE conducts expenditure surveys in metropolitan, micropolitan, and rural areas in the United States. For metropolitan and micropolitan areas, the PSUs are the U.S. Office of Management and Budget’s “core-based statistical areas“ (CBSAs). Counties which are not in a metropolitan or micropolitan CBSA are rural and CE must group these counties into a PSU. For CE, rural PSUs are small clusters of adjacent counties that are required to have a minimum population of 7,500 people and a maximum area of 3,000 square miles. Unlike metropolitan and micropolitan CBSA’s, rural PSU’s are also required to be within a state boundary. Using an adjacency matrix and zero-one integer linear programming, a “first-cut“ assignment of rural counties to a PSU is made. Since the algorithm does not account for geographical obstacles such as rivers and mountains, input from field representatives is used in the final assignment.