Redirected from ERP
Estimated Resident Population (ERP) is the official count of how many people live in Australia. The Australian Bureau of Statistics (ABS) produces it. ERP covers everyone who usually lives here, no matter where they were born. The key idea is usual residence. This means anyone who has lived, or plans to live, in Australia for 12 months or more. For people moving to or from overseas, the ABS uses a "12 out of 16 month" rule to decide if they count. ERP includes people who are briefly abroad. It leaves out short-term visitors.
The starting point is the Census, held every five years. But raw Census counts need fixing. A Post Enumeration Survey measures how many people were missed or counted twice. People who were briefly overseas on Census night are added back. The Census falls in August, but ERP uses a 30 June date, so a small fix bridges the gap.
Between Census years, the ABS updates ERP each quarter at the national and state level. It uses a simple formula.
ERP(t+1) = ERP(t) + Births - Deaths + Net Overseas Migration + Net Interstate Migration
Births and deaths come from state registers. Net overseas migration comes from travel records held by the Department of Home Affairs. Moves between states are tracked with Medicare data.
At the small area level (SA1 and SA2), the ABS works out ERP in a different way. It does not use the formula above for each small area. Instead, it starts with the state-level total and shares it out.
The ABS first works out SA2-level totals. It then splits these across SA1s. To do this, it uses Census counts as a starting point. It then updates them with signals from Medicare address changes and electoral roll data. These signals show where people have moved since the last Census.
This means small area ERP involves more modelling than state-level ERP. The figures are still the best estimates we have, but they are less exact than state or national totals.
ERP figures come out in three tiers. Preliminary figures use early migration data. They come out after about six months. Revised figures use better birth and death data. Final figures use the full window needed to confirm overseas migration. These are the best figures between Census years.
After each Census, the ABS rebases the ERP. It goes back and fixes all the figures since the last Census to line them up with the new count. This gives us the best picture of how the population has changed.
Place Forecast uses SA1-level ERP by single year of age and sex. This is a custom dataset ordered from the ABS. It gives the estimated population figures shown to the left of the jump-off year on charts.
ERP is also the starting point for all projections. The system takes the ERP by age and sex at the jump-off year as its base. Every projected birth, death, and migration event flows from this starting point. How exact the ERP is directly affects how sound every projected number will be.