Transcript 2001 Census Disclosure Control UK variations Frank Thomas GROS General Register Office for SCOTLAND information about Scotland's people.

2001 Census Disclosure Control
UK variations
Frank Thomas
GROS
General Register Office
for
SCOTLAND
information about Scotland's people
Disclosure control for 2001
Scotland
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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)
General Register Office
for
SCOTLAND
information about Scotland's people
Red: UK differences
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)
General Register Office
for
SCOTLAND
information about Scotland's people
ONS increased minimum size of
areas (from 20 households to 40)
• Not much benefit
eg lone Chinese household still a lone
Chinese household
FOR
• Much discontinuity in geog
over 10% OAs would need to be merged
General Register Office
for
SCOTLAND
information about Scotland's people
Small cell adjustment
• Record swapping => intruder can’t be sure
BUT
• ONS worried about perception of identification
(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 disclosure
AND
Upsets users
General Register Office
for
SCOTLAND
information about Scotland's people
What about 2011?
(personal view)
• Geographical continuity
• No SCA
• No record swapping
General Register Office
for
SCOTLAND
information about Scotland's people
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
General Register Office
for
SCOTLAND
information about Scotland's people
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 for
non-household populations
General Register Office
for
SCOTLAND
information about Scotland's people