To make sure the primary suppressions cannot be closely estimated by subtracting the other cells in the table from the marginal totals, additional cells are also suppressed. These additional suppressed cells are called complementary or secondary suppressions. The process of suppression does not change the marginal totals, so the integrity of the data is not adversely affected. Before the Census Bureau releases data, computer programs check published tables for both primary and complementary disclosures. Suppression was used for the 1980 Census of Population and Housing and is now used for economic surveys and censuses.
D indicates data withheld to limit disclosure.
Data swapping is done by editing the source data or exchanging records for a sample of cases when creating a table. Because the swap often occurs within a neighboring area, there is no effect on the marginal totals for the area or for totals that include data from multiple areas. Because of data swapping, users should not assume that tables with cells having a value of one or two reveal information about specific individuals. Data swapping procedures were first used in the 1990 Census, and will be used for Census 2000 and for the Census Bureau's new American Community Survey. For a description of the disclosure limitation procedures used in the economic census and surveys see the discussion on suppression.