Interaction Data
As we saw in Chapter 1, interaction data sets have been derived from a number of sources, including censuses, other surveys and from a range of administrative sources. These typically have the characteristic that the data form large, sparsely populated matrices. Where the matrices do have non-zero values, those numbers are often small. This is highly significant when confidentiality is concerned – small numbers in aggregate data are generally seen as representing an increased risk of disclosure of data. This chapter looks at confidentiality issues with particular regard to interaction data. Different types of disclosure are considered, together with the reasons why interaction data are thought to pose particular disclosure problems. Methods of disclosure control are outlined, and then two particular methods are studied: those used in the 1991 and the 2001 UK Censuses. The methods used and the extent of their effects are described, and suggestions for how best to use the affected data sets are given.