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2001 Census Disclosure Control UK variations

2001 Census Disclosure Control UK variations. Frank Thomas GROS. Disclosure control for 2001 Scotland. Setting a target or average size for output areas (50 households) Setting a minimum size of areas for key output (e.g. 20 households and 50 residents for Census Area Statistics)

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2001 Census Disclosure Control UK variations

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  1. 2001 Census Disclosure ControlUK variations Frank ThomasGROS

  2. Disclosure control for 2001Scotland • Setting a target or average size for output areas (50 households) • Setting a minimum size of areas for key output (e.g. 20 households and 50 residents for Census Area Statistics) • Creating only one set of output areas • Limiting the detail in classifications used in tables • Record swapping before tabulation • Small Cell Adjustment (workplace tables) Red: UK differences

  3. ONS decided to have an average size of around 120 households • Average size for Scottish 1991 output areas was around 55 households So • There would have been much discontinuity in Census geography in Scotland(not a consideration in E&W, NI)

  4. ONS increased minimum size of areas (from 20 households to 40) • Not much benefiteg lone Chinese household still a lone Chinese household FOR • Much discontinuity in geogover 10% OAs would need to be merged

  5. Small cell adjustment • Record swapping => intruder can’t be sure BUT • ONS worried about perception ofidentification (1s) BUT • Actual disclosure a matter of 0s not 1s BUT • SCA increases the perceived number of 0s Decreasing perception of identification increases perception of disclosureANDUpsets users

  6. What about 2011?(personal view) • Geographical continuity • No SCA • No record swapping

  7. What's wrong with record swapping? It is ineffective for • population bases other than the geographical variable being swapped • Had to use SCA for workplace tables • populations for geographies within which records are swapped. • Population uniques still at risk in SARs

  8. Use Over-imputation • It won't amend the area of residence/enumeration (but we could do record swapping as well perhaps) BUT • It can focus on particular areas or variables • It can be pegged back a bit for areas or variables where other processing has wrought much change in the data as collected. • It is better than record swapping fornon-household populations

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