In line with the Methods review outlined above, an investigation of existing methods highlighted an issue with the derivation of age (and consequently age group indexes). The issue related to how age was determined with respect to the current reference week. For example, at the time of the first release on 21 April 2020, there were approximately 509,000 payroll jobs reported to be held by 15-19-year olds in the week ending 14 March 2020. As at the 19 January 2021 release, this cohort was estimated to contain 434,000 payroll jobs for the week ending 14 March 2020.
Previously, a person’s age (and age group) was redefined at each reference week and updated to the start of the time series included in that release. This resulted in the age group population being measured in each reference week changing over time, and becoming increasingly different to the population of interest. This issue particularly impacted the time series of the youngest (aged 15-19 years) and oldest (aged 70 years and over) persons age groups.
In the 2 February 2021 release, the derivation method was updated to: hold a person’s age (and consequently age group) constant until their birthday month; and ‘age’ a person at the start of their birthday month. That is, at the start of each calendar month, the age of all job occupants with a birthday in the coming month will be updated to that of their upcoming birthday.
Privacy protection has been increased by using calendar month to update age, rather than the more precise day and month. However, it may introduce a small amount of volatility in the week on week change at the start of each calendar month. That is, a portion of the movement in age group at the start of the month (payroll jobs and wages) may relate to the ‘aging’ of persons as they transition up an age group.
Indexes for national, state/territory, industry and employment size estimates are not affected by the updated method, as only those indexes with an age dimension have been impacted.
A comparison of payroll jobs is presented in the following graph for the age groups most affected by the change in method, using data from the 2 February 2021 release.