TECHNICAL NOTE


BACKGROUND

Last month's issue of this publication included an article advising that from July 2008 the Labour Force Survey (LFS) sample will be reduced by 24% compared with the June 2008 sample. The article highlighted:

• the reasons for the reduction in sample size;
• the expected sample size in July 2008;
• the impact of the reduced sample size on the quality of the estimates; and
• the impact of the reduced sample size on LFS products and associated surveys.

This article provides information on some of the methodological changes resulting from the reduced sample size.


POPULATION BENCHMARKS

LFS estimates are calculated in such a way as to add up to independent estimates of the civilian population aged 15 years and over (population benchmarks). Currently two sets of population benchmarks are used in producing LFS estimates. The first set of benchmarks are population estimates separated by Capital City, Balance of State, Sex and Age. There are 20 age groups in all; single year groups for those aged 15 to 24, 5 year groups for those aged 25 to 69 and a final group for those aged 70 and over. The second set of benchmarks are population estimates split by Labour Force Dissemination Region and Sex.

The weighting methodology used in the LFS requires a respondent in each of the above benchmarks. An investigation was undertaken to determine the likelihood of no respondents in any of the above benchmarks, given the reduced sample size which will be in place from July 2008.

This investigation found that given the reduced sample size, there would be a high chance of this occurring in the single year age groups (i.e. 15 to 24 years) for balance of South Australia, balance of Western Australia and the city of Hobart. For this reason the ABS has decided to combine some age groups in these areas to significantly lower the likelihood of having no respondents for these groups.

The collapsing of age groups will mean:

• for the balance of South Australia and Western Australia, the single year age groups used for benchmarking will be collapsed to those aged 15, 16, 17, 18-19, 20-21 and 22-24;
• for Hobart the single year age groups used for benchmarking will be collapsed to those aged 15, 16, 17, 18, 19, 20, 21, 22-24.

The decision was made to group the ages together in this way as it keeps the 15 to 19 and 20 to 24 year old age groups separate. This was done because several LFS products are released with that disaggregation.

There will be no other changes to the benchmarks used for other States or Territories or to the age groups used for those aged 25 and above.

The ABS currently releases some products with single year of age data for those aged 15 to 24 years old. The ABS will continue to release all products which contain single year of age data. The quality of these data will be slightly reduced due to the single year of age data no longer being benchmarked in all areas.