EVALUATING LABOUR FORCE SURVEY NON-RESPONSE IMPACT THROUGH IMPUTATION
Operational difficulties during enumeration of the August 2004 Labour Force Survey (LFS) resulted in a much higher number of non-contact households than normal. The August national response rate was just over 94%, more than 2% below the national response rate typically achieved for the LFS.
Analyses were conducted to investigate whether the increased non-response unduly impacted on key estimates. Estimates would have been affected if, on average, the additional non-respondents in August had different labour force characteristics to the persons in the responding sample. Any such differences would have been realised as a change to the non-response bias typically experienced by the LFS, and create a spurious effect in estimates.
A longitudinal imputation procedure was used to estimate the change in non-response bias for labour force status estimates. Since the LFS has high overlap between the set of dwellings selected in consecutive months, it is possible to identify many individuals who were likely in coverage but did not respond to the survey. The imputation procedure imputed persons in non-contact and refusal households who responded to the survey in the previous month. The imputed labour force status was the individual's labour force status in the previous month. Analysis showed the strategy of carrying over the labour force status from the previous month is fairly reliable, with highest error occurring in December and January when many persons enter and leave the labour market. Non-response bias was estimated as the difference between the original estimate and estimate obtained when the imputed persons are included for estimation.
The imputation procedure was applied across the previous 12 months to investigate the recent behaviour of the non-response bias estimates for employed and unemployed. The time series of the non-response bias for the Australian estimate of employed persons was relatively stable until August, when there was a statistically significant change in the bias. The change in bias indicated the August seasonally-adjusted estimate of employed persons was understated by between 15,000 and 25,000 persons. The non-response bias was reflected in the employed estimates at the State and Territory level, with the effect most pronounced in NSW, where August response rates were particularly low. The additional non-response did not significantly affect estimates of unemployed at the Australian or State levels. The imputation results imply that compared to the respondents, the additional non-respondents in August were more likely to be employed and less likely to be not in the labour force.
In the past two months response rates have approached usual levels, and accordingly non-response bias estimates have been close to normal. However, the change back to regular non-response bias levels in September impacted on August-September movements. The imputation procedure could be used in the future on an on-going basis for quality monitoring of the LFS.
For further information, please contact, Julian Whiting on (08) 8237 7362
Email: julian.whiting@abs.gov.au.
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