UK 2001 Census Microdata: Providing Access to Data Subject to Confidentiality Constraints

Disclosure control issues are particularly salient to census microdata release. Data of this type do not benefit from protection arising from small samples. They are derived from the same source as tabular outputs. Additionally, they are subject to statutory requirements above and beyond that of standard data protection. This paper will describe the range of approaches used to ensure that research quality data from the 2001 Census were made available to the research community, following increased concern about confidentiality at the UK census offices. These solutions involved a mixture of broad banding, perturbation, access controls, and differing levels of licensing. A range of microdata are now available. Very detailed files are held in a safe setting; users travel to a secure site and leave outputs to be checked before release. Less detailed files are disseminated to licensed users. Hierarchical household data are subject to a special license.