Statistical methods for some simple disclosure limitation rules

To guard the confidentiality of information provided by respondents, statistical offices apply disclosure limitation techniques. An often applied technique is to ensure that there are no categories for which the population frequency is presumed to be small (‘rare’ categories). This is attained by recoding, top‐coding or setting values to ‘unknown’. Since population frequencies are usually not available, the decision that a category is rare is often based on intuitive considerations. This is a time consuming process, involving many decisions of the disclosure limitation practitioners. In this paper it will be explored to what extent the sample frequencies can be used to make such decisions. This leads to a procedure which enables to automatically scan a data set for rare category combinations, whereby ‘rare’ is defined by the disclosure limitation policy of the statistical office.