The 2011 National Household Survey public use microdata file methodology: How to balance the requirement for more information and the requirement for low risk of disclosure in the microdata

The 2011 National Household Survey (NHS) is a voluntary survey that replaced the traditional mandatory long-form questionnaire of the Canadian census of population. The NHS sampled about 30% of Canadian households and achieved a design-weighted response rate of 77%. In comparison, the last census long form was sent to 20% of households and achieved a response rate of 94%. Based on the long-form data, Statistics Canada traditionally produces two public use microdata files (PUMFs): the individual PUMF and the hierarchical PUMF. Both give information on individuals, but the hierarchical PUMF provides extra information on the household and family relationships between the individuals. To produce two PUMFs, based on the NHS data, that cover the whole country evenly and that do not overlap, we applied a special sub-sampling strategy. Difficulties in the confidentiality analyses have increased because of the numerous new variables, the more detailed geographic information and the voluntary nature of the NHS. This paper describes the 2011 PUMF methodology and how it balances the requirements for more information and for low risk of disclosure.