COMPARING DISABILITY DATA ACROSS COLLECTIONS
The following discussion will examine some important methodological issues that affect comparisons between ABS collections of Aboriginal and Torres Strait Islander disability data.
COMPARING DISABILITY DATA ACROSS DIFFERENT COLLECTION YEARS
Analysis of disability rates for the total Australian population (from 1993 to 2015), demonstrates that changes in disability prevalence over time is generally very slow (analysis available in 4431.0.55.002 – ABS Sources of Disability Information Paper 2012-2016). While there are currently not enough years of data available to demonstrate this trend for disability prevalence in the Aboriginal and Torres Strait Islander population, data from the three most recent SDAC collections suggests that changes in disability prevalence rates for this population are also gradual (see table below).
na not available
(a) All persons. Excludes very remote areas and discrete Aboriginal and Torres Strait Islander communities.
|Disability prevalence rates for the Aboriginal and Torres Strait Islander population - SDAC 2009, 2012, 2015 (a)|
% ± MoE of %
|Severity of Disability|
|Profound core activity limitation|
3.5 ± 0.9
2.8 ± 0.9
|Severe core activity limitation|
4.2 ± 1.2
4.3 ± 1.0
|Total profound/severe core activity limitation|
8.2 ± 1.7
7.8 ± 1.2
7.3 ± 1.4
|Moderate core activity limitation|
2.9 ± 0.9
3.5 ± 1.1
|Mild core activity limitation|
7.2 ± 1.5
7.3 ± 1.5
|Total moderate/mild core activity limitation|
7.0 ± 1.9
10.2 ± 1.5
10.9 ± 1.8
|Education/employment restriction only|
2.8 ± 0.8
3.2 ± 1.2
3.2 ± 1.1
|No specific limitation or restriction |
3.1 ± 1.1
2.3 ± 0.8
3.0 ± 0.9
|Total with disability|
21.1 ± 2.6
23.4 ± 2.0
23.9 ± 2.2
Because of the relative stability of disability prevalence in the population over time, it is possible to compare disability data collected in the SDAC, the Census and the SDM within the 2012-16 reference period, without having to account for large changes in disability prevalence between collections.
COMPARING SURVEY DESIGNS
The way a survey is conducted can affect the number of people identified as having disability. Importantly, responses to a survey can be affected by whether questions are asked in person by an interviewer, or if respondents answer questions for themselves, or others, in an on-line or paper questionnaire.
COMPARING SAMPLE DESIGNS
- 2015 SDAC - Personal interviews are conducted with every member of a household who has been identified as having long term health condition(s) that restricted their living in some way.
- 2012-13 NATSIHS and 2014-15 NATSISS - Respondents are selected for interview following a screening process to identify Aboriginal and Torres Strait islander households (where one or more household members identify as being of Aboriginal or Torres Strait Islander origin). Up to 2 adults and 2 children in non-remote areas, and 1 adult and 1 child in remote areas are selected for face-to-face interviews.
- Census of Population and Housing – Responses are collected via a self-completed online or paper questionnaire. This is generally completed by one person on behalf of the entire household.
The SDAC, NATSIHS and NATSISS are all sample surveys that are weighted to represent larger populations. It’s important to understand that, even in surveys where the target population is the same, sampling variability will occur as each collection draws on a different selection of respondents. Important sampling differences to consider include:
- Sample size - A survey with a large sample size will generally produce estimates with less variability than those with a small sample size. As small population samples are disaggregated further, the variability and errors associated with the data increase proportionately. This is particularly relevant for the SDAC measures of disability for the Aboriginal and Torres Strait Islander population. The sample design for the SDAC does not sample for this population specifically, and is likely to have a small number of Aboriginal and Torres Strait Islander respondents. For a detailed discussion on small samples and associated errors, see Appendix: Impacts of sample size on estimate variability.
- Survey scope and geographic coverage
- The SDAC covers urban and rural areas in all states and territories and includes people living in private dwellings, self-care retirement villages and establishments providing long-term care accommodation. The SDAC sample does not include respondents from discrete Aboriginal and Torres Strait Islander communities or very remote areas. It is estimated that around 2% of the non-remote Aboriginal and Torres Strait Islander population was excluded from the 2015 SDAC sample due to the exclusion of discrete Aboriginal and Torre Strait Islander communities in non-remote areas. Another 12% were excluded due to the omission of very remote areas of Australia from the sample for this survey.
- The 2012-13 NATSIHS and 2014-15 NATSISS produce reliable estimates for the Aboriginal and Torres Strait Islander population at the national level, for each state and territory and all remoteness areas (including community samples of discrete Aboriginal and Torres Strait Islander communities). These surveys collect information from respondents in private dwellings only and do not include any establishments.
Additionally, when comparing Aboriginal and Torres Strait Islander disability data specifically, it is important to consider the impact that differences in the propensity to identify can have on samples across time and survey collections. For further information on sample survey methodology see ‘Understanding Statistics
’ on the ABS website.