4720.0.55.002 - Microdata: National Aboriginal and Torres Strait Islander Social Survey, 2014-15 Quality Declaration 
Latest ISSUE Released at 11:30 AM (CANBERRA TIME) 27/05/2016  First Issue
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FILE STRUCTURE

Data available by level

The 2014–15 National Aboriginal and Torres Strait Islander Social Survey (2014–15 NATSISS) microdata is available across three levels. Some of these levels have a hierarchical relationship:

1. Household level
3. Selected person level
4. Barriers to services level


Broadly, each level provides the following:
  • Household level — characteristics of the household, such as size and structure of the household, household income, household facilities and costs, household financial stress, household smoking and transport details
  • Selected person level — all demographic and socio-economic characteristics of the survey respondents, and most of the information they provided
  • Barriers to services level — information about the types of services that were difficult to access and the reasons why they were described as difficult

An additional level (2. All persons in household) was created for processing purposes, including family coding and calculating household income. Data from this level is not available for output.


General Social Survey (Non-Indigenous) — (TableBuilder only)

The 2014 General Social Survey (Non-Indigenous) (2014 GSSNI) TableBuilder is constructed as a subset from the 2014 General Social Survey (GSS) TableBuilder, which has been modified to reflect the NATSISS file structure and comparable data items. This will enable comparisons between Aboriginal and Torres Strait Islander and non-Indigenous social outcomes using 2014–15 NATSISS and 2014 GSSNI data.

As a modified version of the GSS TableBuilder file, The 2014 GSSNI TableBuilder file contains the following key features:
  • Retained GSS data items common to both NATSISS and GSS
  • Removal of persons of Aboriginal and Torres Strait Islander origin
  • Removal of households where any person in the household was of Aboriginal or Torres Strait Islander origin (i.e. the if the selected person was non-Indigenous, but another household member was of Aboriginal or Torres Strait Islander origin, then the household was removed.)

For further information regarding the GSS TableBuilder see Microdata: General Social Survey, Australia, 2014 (cat. no. 4159.0.30.004).


Weights and estimation

As the NATSISS survey was conducted on a sample of households in Australia, it is important to take account of the method of sample selection when deriving estimates. This is particularly important as a person's chance of selection in the survey varied depending on the state or territory in which they lived. Survey 'weights' are values which indicate how many population units are represented by the sample unit.

There are two survey weights provided: a person weight (ISSFINWT) and a household weight (HHFINWT). These should be used when analysing data at the person and household level respectively.

Where estimates are derived, it is essential that they are calculated by adding the weights of person or households, as appropriate in each category, and not just by counting the number of records falling into each category. If the 'weight' of each person or household were to be ignored, then no account would be taken of a person or household's chance of selection in the survey or of different response rates across population groups, with the result that counts produced could be biased. The application of weights ensures that person and household estimates conform to an independently estimated distribution of the population by state, remoteness, age, sex and remote community status.

General Social Survey (Non-Indigenous) — (TableBuilder only)

For the 2014 GSSNI TableBuilder, weights for applicable household, person and access to services level records were retained from the GSS Tablebuilder. For information about weighting of the GSS file, see the File structure page from Microdata: General Social Survey, Australia, 2014 (cat. no. 4159.0.30.004).


Counting units and weight

The counting unit for NATSISS level one is the household, for level three the person, for level four barriers to services. There is a weight attached to each level in order to estimate the total population of the respective counting unit. The weight on level one is the household weight, and the weight for levels three and four is the person weight.

What you count depends on the level from which you select the weight. A household level weight estimates the number of households with a particular characteristic. Likewise the weight included in the person level estimates the number of persons with the selected characteristics. Replicate weights have also been included and these can be used to calculate the standard error. For more information, refer to the Standard Errors section below.

General Social Survey (Non-Indigenous) — (TableBuilder only)

For the 2014 GSSNI TableBuilder, counting units and weights were retained from the GSS TableBuilder. For information about weighting of the GSS file, see the File structure page from Microdata: General Social Survey, Australia, 2014 (cat. no. 4159.0.30.004).


Standard errors

Each NATSISS record on the household level and person level also contains 250 replicate weights and, by using these weights, it is possible to calculate standard errors for weighted estimates produced from the microdata. This method is known as the 250 group delete-a-group jack-knife variance estimator.

Under the delete-a-group jack-knife method of replicate weighting, weights were derived as follows:
  • 250 replicate groups were formed, with each group formed to mirror the overall sample. Units from a cluster of dwellings all belong to the same replicate group, and a unit can belong to only one replicate group
  • For each replicate weight, one replicate group was omitted from the weighting and the remaining records were weighted in the same manner as for the full sample
  • The records in the group that was omitted received a weight of zero
  • This process was repeated for each replicate group (i.e. a total of 250 times)
  • Ultimately each record had 250 replicate weights attached to it with one of these being the zero weight

Replicate weights enable variances of estimates to be calculated relatively simply. They also enable unit record analyses such as chi-square and logistic regression to be conducted, which take into account the sample design. Replicate weights for any variable of interest can be calculated from the 250 replicate groups, giving 250 replicate estimates. The distribution of this set of replicate estimates, in conjunction with the full sample estimate, is then used to approximate the variance of the full sample.

The formulae for calculating the Standard error (SE) and Relative standard error (RSE) of an estimate using this method is shown below.

Formula for calculating the Standards error and Relative standard error

RSE(y) = SE(y)/y*100

where:

g = (1, ..., 250) (the number of replicate weights)

y(g) = estimate from using replicate weighting

y = estimate from using full person weight.


The delete-a-group jack-knife method can be applied not just to estimates of the population total, but also where the estimate y is a function of estimates of the population total, such as a proportion, difference or ratio. For more information on the delete-a-group jack-knife method of SE estimation, see Research Paper: Weighting and Standard Error Estimation for ABS Household Surveys (Methodology Advisory Committee), July 1999 (cat. no. 1352.0.55.029).

Use of the 250 group delete-a-group jack-knife method for complex estimates, such as regression parameters from a statistical model, is not straightforward and may not be appropriate. The method as described does not apply to investigations where survey weights are not used, such as in unweighted statistical modelling.

General Social Survey (Non-Indigenous) — (TableBuilder only)

For the 2014 GSSNI TableBuilder, the weighting methodology was retained from the GSS TableBuilder. The main difference from the NATSISS being that the 2014 GSSNI contains 60 replicate weights. For information about weighting of the GSS file, see the File structure page from Microdata: General Social Survey, Australia, 2014 (cat. no. 4159.0.30.004).