2970.0.55.017 - 2001 Census of Population and Housing - Fact Sheet: Confidentiality of Census Output, 2001  
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 03/06/2002  First Issue
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Confidentiality of Census Output

The guarantee of the Act

The census collects information relating to each person and household in Australia. It is taken to provide a snapshot of information about the community as a whole and about groups within the community. However it is not concerned with information about individuals as such. The public expects that the information they provide will be kept confidential, and this is ensured by provisions in the Census and Statistics Act 1905. Under this Act, all ABS officers are legally bound never to release identifiable personal information to any person or organisation outside the ABS.

Section 19 of the Act makes it an offence for any past or present ABS officer to divulge, either directly or indirectly, any confidential information collected under this Act. The penalty for this offence is a fine of up to $5,000 or imprisonment for a period not exceeding two years, or both.

In accordance with the Act, no results will be released in a way which would enable particular individuals or households to be identified. In addition, the ABS is obligated to comply with the principles set out under the Privacy Act 1988.

This fact sheet covers the following issues:

  • security arrangements;
  • retention of name-identified information; and
  • confidentiality of tabular data.

Security arrangements during collection and processing

Completed census forms will be transferred from the collection centres to the census data processing centre under secure arrangements. Full-time security personnel will be employed to prevent any unauthorised access to the processing centre.

Comprehensive security arrangements are implemented on the ABS computer system. These include the use of regularly changed passwords, access control and audit trails.

Retention of name-identified information

All name identified information from past censuses has been destroyed, once the statistical processing was completed. However, for the 2001 Census, not all name-identified information will be destroyed:
  • The Government has accepted the recommendation of the Standing Committee on Legal and Constitutional Affairs report, Saving Our Census and Preserving Our History that saving name-identified census information 'for future research, with appropriate safeguards, will make a valuable contribution to preserving Australia's history for future generations'. This is particularly true for the 2001 Census as it coincides with the Centenary of Federation.
  • In order to ensure the current high levels of public confidence and cooperation in the census are maintained, and to respect the wishes of those who do not want their information retained for future release, information will only be kept for those persons who explicitly give their consent. If a person does not explicitly agree to their name-identified Census information being retained their name and address will be destroyed once statistical processing has been completed.
  • The name-identified information that is kept will not be available for any purpose including by a court or tribunal within a 99 year closed access period. It will become publicly available in the year 2100.


Confidentiality of tabular data

Tables containing cells with very small counts may potentially result in identifiable information. To avoid releasing identifiable information all tables are subjected to two confidentiality processes before release:
  • Assessing the size of the table; and
  • introduced random error.

These steps are taken to avoid releasing information that may identify particular individuals, families, households or dwellings without impairing the usefulness of the tables.


1. Assessing the size of the table

This process compares the total number of cells in a table to the total population for that table. The total number of cells may include categories such as 'Not stated', 'Not applicable', and 'Inadequately described'.

If the number of cells is the same as, close to, or exceeds the population size, then the table will not be released. This practice avoids the release of tables containing a large proportion of small cells containing identifiable data.


Example 1
A table of 3 variables cross-classified

VariableNumber of
Categories
Sex
2
Labour Force Status
5
SLAs in Sydney SD
46

This table would result in 460 theoretical cells (i.e. 2 x 5 x 46). The population for this table is 2,942,389 persons. Therefore this table may be released.



Example 2
Another table of 3 variables cross-classified

VariableNumber of
Categories
Sex
2
Occupation
445
CDs in Sydney SD
6,542

This table would result in 5,822,380 theoretical cells (i.e. 2 x 445 x 6,542). The population for this table is 2,942,389 persons. Therefore this table would not be released.

If you are unsure whether a table can be released, please contact ABS Information Consultancy.


2. Introduced Random Error

A technique has been developed to avoid identification of individuals. The confidentiality technique applied by the ABS is to randomly adjust cells with very small values. These adjustments do not impair the value of the table as a whole. The technique allows very large tables, for which there is a strong client demand, to be produced even though they contain numbers of very small cells. It is ABS policy not to release the detailed methodology employed by the ABS to adjust the data.

Tables which have been randomly adjusted will be internally consistent, however comparisons with other tables containing similar data may show minor discrepancies. This is the case for both customised tables and standard products. These small variances can, for the most part, be ignored.

Care should be taken when specifying tables to minimise the number of small cells. No reliance should be placed on small cells. Aside from the effects of introduced random error, possible respondent and processing errors have greatest relative impact on small cells.

More information on random error can be found in the 2001 Census Dictionary (Cat. no. 2901.0), on page 218 in 'Introduced random error'.