Protecting privacy when releasing statistical information: small value suppression

​​The Government of Canada has provided guidance on protecting privacy when releasing information about a small number of individuals. This guidance explains that there is a potential risk of identifying individuals by using a statistical report either “alone or in combination with other sources of information.”

When publishing statistics on Immigration and Refugee Board of Canada (IRB) proceedings before the Refugee Protection Division (RPD) and the Refugee Appeal Division (RAD), small value suppression is applied by the IRB to data values less than 20, by replacing that value with the notation "--". This risk mitigation strategy is applied to IRB statistical reports to protect the privacy of those who appear before the Board as refugee protection claimants. Suppressing small values in these reports reduces the risk that individuals who are the subject of what are overwhelmingly private proceedings could be identified.

Examples of small value suppression

IRB statistical reports on the RPD and the RAD produced for release have a minimum value of 20. The IRB also ensures that a suppressed value cannot be derived from subtracting the sum of the non-suppressed values from a total or subto​tal. Therefore, in reports where a sum is provided along with all its addends, and a suppression is required, both the lowest and second lowest addend are supressed.

Unsuppressed data

Group 13041252620475
Group 2284571292
Group 37029721127
Group 4531110

Suppressed data

Group 13041252620475
Group 22845----92
Group 37029----127
Group 4----------
  • Group 1: No suppression required as all values have a minimum value of 20
  • Group 2: Two values are below 20, and both require suppression
  • Group 3: Only one value is under 20; however, the second lowest addend also needs to be supressed
  • Group 4: All values are under 20, and therefore supressed