idc-logo
svg rectangle color
City of JoondalupCommunity profile

City of Joondalup

Data confidentiality

The information presented in the tables in profile.id is based on detailed tables produced by the Australian Bureau of Statistics (ABS) at the Local Government Area level, and at other geographic levels including SA2, SA1, Suburb and Locality, State and Commonwealth electoral divisions for all non-LGA level datasets. These geographic areas apply to 2021, 2016 and 2011 data. Prior to that, combinations of Census Collection District (CDs) are used.

The ABS adjusts information it provides in tables to preserve the confidentiality of individuals. All cells are slightly adjusted to prevent any identification of personal details. Methodologies for doing this have changed several times in the last 30 years, and confidentiality rules for each Census period shown are those that applied at the time.

Data tables released prior to the 2006 Census had small numbers (values of 1 or 2) randomly adjusted to either 0 or 3 by the ABS. As tables are randomly adjusted independently of each other, totals differ slightly across tables with the same population, however for 2001 and earlier, all numbers larger than 3 can be assumed to be exact and unchanged between different tables.

For the 2006 and 2011 Census, a different method called "perturbation with additivity" was used. All figures included within any table may be randomly adjusted by a small amount. These adjustments result in small introduced random errors. This method was introduced so that individuals not be directly identified in the data and "differencing" could not be employed to derive individual characteristics. These random adjustments were balanced out across the table, so the totals were consistent across the categories. (ie. A random decrease in one category was matched by a random increase in another, to balance out the table.) This was known as the additivity process.

For the 2016 and 2021 Census, a different method is used, called "perturbation without additivity". Adjustments to all cells in a table are possible, but small cells are randomly "suppressed" or changed to zero. This has the common (but not universal) effect of reducing the table total when derived by adding up rows and columns. Whereas prior Censuses had table totals which could be slightly higher or lower than the actual total due to random adjustment, the 2016 and 2021 Census table totals will usually be equal to or lower than the actual unadjusted total, due to this suppression. This has a significant effect on tables with a large number of categories, such as Birthplace and Language, and geographic areas built from smaller geographic areas, such as some small areas which are built from SA1s.

While the ABS now publish table totals separately at the bottom of each table, which are closer to the "true" population, these aren't used on profile.id, as the percentages derived from them will not add to 100% and could not be compared to earlier years.

The effect of this on the profile.id site is that the totals derived by summing rows and columns will differ slightly from those provided by the ABS but will add to 100%. .id has been through a process between 2016 and 2021 Census years of adjusting most of the community sites to use larger geographic units not derived from smaller areas (eg. SA1s) and ordering larger aggregate category date (eg "Total overseas born") directly from the ABS so it’s subject to less perturbation without additivity. So this issue should be less severe in most areas compared to when the 2016 data were launched.

Although the information value of the table as a whole is not impaired by permutation, care should be taken when interpreting very small numbers, since randomisation will affect the relative size of small numbers far more than larger numbers. The effect of the randomisation methodology also ensures that values of 1 and 2 do not appear in tables. For this reason, display tables with many categories – such as birthplace, language and religion groupings – only show populations down to a minimum population of 10 people. This minimises the relative effect of perturbation and includes only numbers which are less susceptible to Census non-sampling error anyway.

No reliance should be placed on small cells as they are impacted by adjustment, respondent and processing errors. Rather than adding up totals from small areas to derive LGA totals, please use the LGA total provided on the site. Small area totals may also differ compared to downloading the equivalent dataset directly from the ABS website, due to geographic differences and differences in the level at which permutation is applied.

This level of compromise should not impact on decision makers making effective resource-allocation and planning decisions.

DISCLAIMER: While all due care has been taken to ensure that the content of this website is accurate and current, there may be errors or omissions in it and no legal responsibility is accepted for the information and opinions in this website.

Please view our Privacy Policy, Terms of use and Legal notices.

ABS Data and the copyright in the ABS Data remains the property of the Australian Bureau of Statistics. The copyright in the way .id has modified, transformed or reconfigured the ABS Data as published on this website remains the property of .id. ABS Data can be accessed from the Australian Bureau of Statistics at www.abs.gov.au. ABS data can be used under license - terms published on ABS website. intermediary.management@abs.gov.au if you have any queries or wish to distribute any ABS data.