What does a National Forecasting Program version number mean?

The National Forecasting Program (NFP) version number tells you which input data a forecast is based on and how many times each tier of the forecast has been updated. The format reflects the tiered way the forecast is built, from the national level down to small areas. This article explains what each part of the number means and how to read it.

Key concepts

How the forecast is built

The National Forecasting Program produces forecasts at a national level all the way down to micro geography. It does this in three tiers, combining a top-down approach with a bottom-up approach.

The top-down forecast cascades population down through larger geographies. .id produces an annual update to the national forecast and to every state and territory, by sex and single-year-of-age, over a 25-year horizon. This is followed by an annual update of the state and territory forecast down to Statistical Area Level 4 across the country. Together these two tiers cascade the Estimated Resident Population down from the national level.

The bottom-up forecast is the third and final tier. It forecasts from Statistical Area Level 4 down to a micro geography, usually Statistical Area Level 1 or smaller where available. At this tier, dwelling supply is mapped and dwelling demand is assessed to build the forecast from the ground up.

Terms used in the version number

Census year is the year of the census that informs the base data for the forecast.

Estimated Resident Population (ERP) is the official Australian Bureau of Statistics (ABS) measure of how many people usually live in an area. The version number records the most recent year of ABS ERP data, sourced from the ABS Regional Population release, used in the forecast.

Statistical Area Level 4 (SA4) and Statistical Area Level 1 (SA1) are standard ABS geographies. SA4 is a large regional geography. SA1 is one of the smallest, covering roughly 200 to 800 people. Micro geography means SA1 or a smaller area where data allows.

How to read a version number

You will now see forecast versions in a five-part format, for example 2021.2024.3.1.1.

Each part maps to a tier of the methodology:

[census year].[year of latest historic ERP].[version of AUS to STE].[version of STE to SA4].[version of SA4 to micro geography]

Reading the example 2021.2024.3.1.1 from left to right:

2021 is the year of the census informing the forecast base data.
2024 is the year up to and including which ABS-sourced Estimated Resident Population figures, from the Regional Population release, have been used.
3 is the version of the national to state and territory forecast. In this case it is the third release on the same underlying data.
1 is the version of the state and territory down to Statistical Area Level 4 forecast. This is the first release.
1 is the version of the Statistical Area Level 4 down to micro geography forecast. This is also the first release.

Each tier carries its own version number so you can see exactly which part of the forecast has been updated and which input data it draws on.

The versioning was updated to make the tiered methodology of the National Forecasting Program explicit, and to help you understand which input data a forecast is based on.

Frequently asked questions

Q: Why did the version number format change?

A: The earlier format did not show how the forecast is built. The five-part format makes the tiered methodology visible and tells you which input data, the census year and the latest ABS ERP year, each forecast draws on.

Q: Which number changes when a new forecast is released?

A: It depends on which tier was updated. The first number changes only when a new census is conducted, its data is released by the ABS and we incorporate it as new base data. This happens every five years. The second number updates annually, when we run the top-down forecasts and pick up the latest ERP release from the ABS. The third, fourth and fifth numbers change when the first two numbers change (a first release), or when we republish a tier to correct an inconsistency or error.

Q: Does a higher version number mean the forecast is more accurate?

A: Not on its own. A higher tier version number means that tier has been rerun more times, often to incorporate new dwelling or development information. Accuracy depends on the input data, which the census year and ERP year in the version number describe.

Q: How do I know if two forecasts use the same base data?

A: Compare the first two numbers. If the census year and the latest historic ERP year match, both forecasts share the same base data, even if the later tier version numbers differ.

Q: A suburb (SAL) or LGA is made up of several SA4s. Which version applies?

A: Suburb and Locality (SAL) and LGA areas don't follow the ABS forecast geographies, so their figures are aggregated from the SA1s inside them. Where an area draws on more than one SA4, the version shown reflects the most recent contributing SA4 update.