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This Frequently Asked Questions (FAQs) page addresses some specific issues relating to SEIFA 2011. Answers to some more general FAQs relating to SEIFA are available on the Census pages.
Are the methods used to produce SEIFA 2011 the same as for past releases of SEIFA?
The methods used are generally the same, however there has been a small but positive refinement to the exclusion rules to ensure a reliable index score is obtained for as many areas as possible. Exclusion rules determine which areas do not receive an index score because of low populations or poor quality data.
Due to the refinement of the exclusion rules, an area can receive an index score for one index and not another depending on the make-up of its variables. For SEIFA 2006, if an area did not receive an index score, it did not receive an index score for any of the four indexes.
How does the ABS define advantage and disadvantage for SEIFA 2011?
For the purpose of SEIFA, the ABS continues to broadly define relative socio-economic advantage and disadvantage in terms of people's access to material and social resources, and their ability to participate in society.
This is the same definition used in SEIFA 2006.
Have there been any changes to the variables considered for inclusion in the indexes?
Although Census 2011 collected the same variables as Census 2006, some newly derived SEIFA variables have been considered (children in jobless families, unengaged youth), and a number of variables (related to household tenure, education and internet access) have had some definitional changes. Some variables were also updated in line with updated classification standards. Variables using cut-off values in their definitions, such as high and low income, were updated appropriately.
Of particular note to users of past versions of SEIFA, the IRSD no longer contains the variable relating to the proportion of people identifying as Indigenous in an area. More information on this issue can be found in Section 3.5.3 of the SEIFA 2011 Technical Paper.
Are there any changes in the way SEIFA is presented in the output spreadsheets?
More information on the distribution of SA1 scores within larger areas has been included in the output spreadsheets to enable more informative and detailed analyses. For a more detailed description of this new output, please see Data.
How can I map SEIFA 2011?
For the first time, SEIFA has been released in KMZ format. These files can be read into Google Earth® to provide thematic maps of the four indexes at different geographical levels. For more information, please see Mapping with Google Earth®.
Why are there two SA1 codes on the SA1 level thematic maps?
Between 2006 and 2011 Censuses the Australian Standard Geographic Classification (ASGC) was replaced by the Australian Statistical Geography Standard (ASGS) which is the Australian Bureau of Statistics' new geographical framework. This means that the base geographic area used in SEIFA has changed from Census Collection District (CD) to Statistical Area Level 1 (SA1).
SA1s are not named. They are identified either by an 11-digit fully hierarchical code, or by a truncated 7-digit code comprising the State and Territory (S/T), Statistical Area Level 2 (SA2) and SA1 identifiers. The truncated 7-digit codes are used for the SEIFA datacubes for consistency with other Census products, however the 11-digit code is also included on the thematic maps.
For more information on Statistical Area Level 1s, please see the ASGS page.
What is the difference between area-based and population-based SEIFA deciles?
Area-based and population-based SEIFA deciles are two different measures and have different uses in analysis.
Area-based deciles are calculated by dividing the areas, ordered by disadvantage with 1 representing the most disadvantaged area, into 10 equally sized groups. Area-based deciles are easy to interpret as SEIFA is designed and constructed as an area-based measure. This compares to population-based deciles which are calculated by dividing SEIFA areas into 10 equal groups in such a way that the population in each group is approximately equal. Due to SEIFA being created at an area level, there will still be some clumping of the population so the population based deciles will not be exactly a tenth of the population. Population-based deciles can be difficult to interpret as SEIFA is designed as an area-based measure. The population in the most disadvantaged population-based decile is the 10% of the national population residing in the most disadvantaged areas, rather than the most disadvantaged 10% of the population. This is due to SEIFA measuring the characteristics of an area rather than of individuals.
An example of data organised into area- and population-based deciles is provided in Table 1. The calculation for area- and population-based deciles are:
Calculation for Area-based Deciles:
As shown in the table, there are 30 ranked areas in total. Therefore the number of areas in each area-based decile should be 3.
Calculation for Population-based Deciles:
We firstly sum up the population of each area to get the total population which is 13857 in this example. This indicates that the approximate population for each population-based decile should be 1386 which is 13857 divided by 10 in this example. We then start to group deciles from area 1 to ensure the total population in each group is as close to 1386 as possible.
Table 1: Areas and their SEIFA scores and population (entries for illustration purposes only)
When choosing which measure to adopt, a key consideration would be the spread of the population across the areas and whether it would be beneficial to analyse equally sized population groups. The choice is determined by the type of analysis being undertaken and the proposed use. This may be relevant for more aggregated geographical levels which have a less uniform distribution of the population in each area (e.g. Local Government Areas which range in population size from several thousand to two million). In this situation, creating population-based deciles provides a more uniform distribution of the population across deciles and may be preferred depending on the analysis.
More information on this issue can be found in Section 6.6 of the SEIFA 2011 Technical Paper.
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