Definition: Threshold rule
Usually, with the threshold rule, a cell in a table of frequencies is defined to be sensitive if the number of respondents is less than some specified number. Some agencies require at least five respondents in a cell, others require three. When thresholds are not respected, an agency may restructure tables and combine categories or use cell suppression, rounding or the confidentiality edit, or provide other additional protection in order to satisfy the rule.
ESSNet SDC (Network of Excellence in the European Statistical System in the field of Statistical Disclosure Control), under the coordination of Anco HUNDEPOOL, "Handbook on Statistical Disclosure Control", version 1.2 (2010 Edition)