WEIGHTS AND ESTIMATION
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WEIGHTS AND ESTIMATION
As the 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 from the CURF. 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.
Each person record contains two weights, a Labour Force Survey (LFS) weight called LFSWTD and a Labour Mobility Survey weight called FINPRSWT. These weights indicate the number of people in the civilian population represented by that person. There are two weights because the scope of the LFS is different to the scope of the Labour Mobility Survey. For data items that are only applicable to the Labour Mobility Survey, it is important to use the Labour Mobility Survey weight, FINPRSWT. Users should take care to ensure the appropriate weight is used for analysis. The Data Items List is available on the Downloads tab.
The LFS weight, LFSWTD, is available on all records on the CURF. The Labour Mobility Survey weight, FINPRSWT, appears on 32,119 records. The estimates in the Labour Mobility Survey publication are based on a subset of these records, that is persons who worked at some time during the year ending February 2012. Therefore when using FINPRSWT, in order to match published Labour Mobility Survey estimates, the filter CURFPOP1=1 must be used.
Where estimates are derived from the CURF, it is essential that they are calculated by adding the weights of persons in each category and not just by counting the number in each category. If each person's 'weight' is ignored, then no account would be taken of a person's chance of selection or of different response rates across population groups, and the resulting estimates could be significantly biased and would only represent distributions within the actual selected sample and not the population of interest. The application of weights will ensure that the subsequent estimates conform to an independently estimated distribution of the population by age and sex, rather than to the age and sex distribution within the sample itself.
For further information see the Explanatory Notes in the publications Labour Force, Australia (cat. no. 6202.0) and Labour Mobility, Australia, February 2012 (cat. no. 6209.0).
Standard errors for each estimate produced from this CURF can be calculated using the replicate weights provided on the file.
Each person record contains two sets of 30 replicate weights. Replicate weights applicable to LFS data items contain the prefix 'WPM01' and those applicable to Labour Mobility Survey data items contain the prefix 'WPX02'. By using these weights, it is possible to calculate standard errors for weighted estimates produced from the microdata. This method is known as the 30 group Jack-knife variance estimator. For data items that are only applicable to the Labour Mobility Survey, refer to About the Data Items List.
Under the Jackknife method of replicate weighting, weights were derived as follows:
- 30 replicate groups were formed with each group formed to mirror the overall sample (where units from a collection district all belong to the same replicate group and a unit can belong to only one replicate group)
- one replicate group was dropped from the file and then the remaining records were weighted in the same manner as for the full sample
- records in that group that were dropped received a weight of zero.
This process was repeated for each replicate group (i.e. a total of 30 times). Ultimately each record had 30 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 records 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 30 replicate groups, giving 30 replicate estimates. The distribution of this set of replicate estimates, in conjunction with the full sample estimate (based on the general weight) is then used to approximate the variance of the full sample.
To obtain the standard error of a weighted estimate y, the same estimate is calculated using each of the 30 replicate weights. The variability between these replicate estimates (denoting y(g) for group number g) is used to measure the standard error of the original weighted estimate y using the formula:
g = the replicate groups
y(g) = the weighted estimate, having applied the weights for replicate group 'g'
y = the weighted estimate from the full sample.
The 30 group Jack-knife method can be applied not just to estimates of population total, but also where the estimate y is a function of estimates of population total, such as a proportion, difference or ratio. For more information on the 30 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 30 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.
The following table has been provided to enable CURF users to check some of the relative standard errors they have produced.
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Persons who were working at February 2012 aged 15 years and over, Duration and change in employer/business
Relative Standard Error
|Duration with employer/business at February 2012 |
|Under 12 months |
|Under 3 months |
|3 and under 6 months |
|6 and under 12 months |
|One year or more with current employer/business |
|1 and under 2 years |
|2 and under 3 years |
|3 and under 5 years |
|5 and under 10 years |
|10 and under 20 years |
|20 years and over |
|Whether changed employer/business in the last 12 months (a) |
|Changed employer/business in the last 12 months |
|Did not change employer/business in the last 12 months |
|(a) Refers only to persons who have worked with their current employer/business for less than 12 months. |
Many data items included in the microdata include a 'Not applicable' category. The classification value of the 'Not applicable' category, where relevant, are shown in the relevant data item lists available on the Downloads