POPULATION GLOSSARY

Dependency ratio

The dependency ratio is a measure used to compare the size of the working age population to the size of the non-working age population, calculated as the sum of people aged 0-14 and 65 years and over (that is, 'dependents') divided by the number of people aged 15-64 years, multiplied by 100.

Estimated resident population (ERP)

ERP, the official measure of the population of Australia, is based on the concept of residence and was introduced in 1971. Prior to 1971, estimates of the population were based on the number of people actually present in Australia. ERP refers to all people, regardless of nationality or citizenship, who usually live in Australia, with the exception of foreign diplomatic personnel and their families. It includes usual residents who are overseas for less than 12 months. It excludes overseas visitors who are in Australia for less than 12 months.

Estimates of the Australian resident population are generated on a quarterly basis by adding natural increase (the excess of births over deaths) and net overseas migration (NOM) occurring during the period to the population at the beginning of each period. This is known as the cohort component method and can be represented by the following equation:

P_(t+1) = P_(t) + B - D + NOM

where P_(t) is the estimated resident population at time point t, P_(t+1) is the estimated resident population at time point t+1, B is the number of births occurring between t and t+1, D is the number of deaths occurring between t and t+1, and NOM is the net overseas migration occurring between t and t+1.

For state and territory population estimates, an additional term is added to the equation representing net interstate migration occurring between t and t+1, represented by the following equation:

P_(t+1) = P_(t) + B - D + NOM + NIM

Natural increase

Excess of births over deaths.

Net overseas migration (NOM)

Net overseas migration is the net gain or loss of population through immigration to Australia and emigration from Australia. It is:

• based on an international traveller's duration of stay being in or out of Australia for 12 months or more;
• the difference between the number of incoming travellers who stay in Australia for 12 months or more, who are not currently counted in the population, and are then added to the population (NOM arrivals); and the number of outgoing travellers (Australian residents and long-term visitors to Australia) who leave Australia for 12 months or more, who are currently counted within the population, and are then subtracted from the population (NOM departures).

The current method for estimating net overseas migration is based on a traveller's actual duration of stay or absence using the 12/16 rule, i.e. the duration of stay or absence does not have to be continuous and is measured over a 16 month period . Preliminary estimates are modelled on patterns of traveller behaviours observed in final NOM estimates for the same period one year earlier (for more information refer to ABS Australian Demographic Statistics, cat. no. 3101.0 or ABS Migration, Australia, cat. no. 3412.0).

Estimates for September quarter 2006 onwards use an improved methodology; caution should be exercised when comparing estimates over time.


Population growth

The sum of natural increase and net overseas migration.

Population projections

ABS population projections are not predictions or forecasts, but are simply illustrations of the growth and change in population which would occur if certain assumptions about future levels of fertility, mortality, internal migration and overseas migration were to prevail over the projection period. Three main series of projections, Series A, B and C, have been selected from a possible 72 individual combinations of the various assumptions. Series B largely reflects recent trends in fertility, life expectancy at birth, net overseas migration and net interstate migration, whereas Series A and Series C are based on high and low assumptions for each of these variables respectively.

Series A

• a total fertility rate of 2.0 babies per woman from 2021 onwards,
• life expectancy at birth increasing to 93.9 years for males and 96.1 years for females by 2056 and remaining constant thereafter,
• net overseas migration of 220,000 people per year from 2011 onwards.

Series B

• a total fertility rate of 1.8 babies per woman from 2021 onwards,
• life expectancy at birth increasing to 85.0 years for males and 88.0 years for females by 2056 and remaining constant thereafter,
• net overseas migration of 180,000 per year from 2008 onwards.

Series C

• a total fertility rate of 1.6 babies per woman from 2021 onwards,
• life expectancy at birth increasing to 85.0 years for males and 88.0 years for females by 2056 and remaining constant thereafter,
• net overseas migration of 140,000 per year from 2011 onwards.

Total fertility rate (TFR)

The sum of age-specific fertility rates (live births at each age of mother per female population of that age). It represents the number of children a female would bear during her lifetime if she experienced current age-specific fertility rates at each age of her reproductive life.