Estimated Resident Population (ERP)
The Estimated Resident Population (ERP) is the official measure of population, used as the base (starting) population for Victoria in Future projections.
The ERP is based on the concept of usual residence. It is derived from the count from the latest Census, with the addition of quarterly components of population growth (births, deaths, population movements). It incorporates the estimated Census net undercount (to account for people who were missed from or counted more than once in the Census) and is adjusted to include usual residents who were temporarily overseas at the time of the Census and to exclude overseas visitors who were temporarily in Australia on Census night.
The ABS produces ERPs for Australia, its states, territories and sub-state/territory regions and for local government areas (ABS cat. no. 3301.0, 3218.0 and 3235.0 respectively). Australian and state data is published quarterly, with a yearly age/sex distribution. Sub-state data is published annually, with a 5-year-age group/sex distribution.
Census population counts
The Census of Population and Housing is conducted every five years under the Census and Statistics Act 1905 and aims to measure accurately the number of people and dwellings in Australia on Census night, and a range of their key characteristics. The most recent Census of Population and Housing was conducted on 9 August 2011. The Census contains two measures of population,
- Population by place of enumeration, based on where people were on Census night,
- Population by place of usual residence, based on people’s declared usual address.
In contrast with the Estimated Resident Population, the Census population includes short-term visitors and excludes people temporarily absent from Australia.
Victoria in Future projections are an estimate of the future size, distribution and composition of the population. They are developed using mathematical models and expert knowledge, relying on trend analysis and assumptions about future change. VIF2019 is not an exact predication or forecast of the future.
Uncertainty about the future increases over longer projection horizons and with smaller geographic disaggregations. Different policy settings and changes in the economy could result in changes to the expected size, distribution and characteristics of the population.
Components of population change
Births and Deaths
The births and deaths data used in VIF2019 are consistent with those used in the ABS resident population estimates, based on usual residence and year of occurrence.
Natural increase is the difference between the number of births and deaths occurring during the period. If the number of deaths exceeds the number of births, it is called natural decrease.
Net overseas migration (NOM)
NOM is the difference between the number of incoming travellers who stay in Australia for 12 months or more and are added to the population (NOM arrivals) and the number of outgoing travellers who leave Australia for 12 months or more and are subtracted from the population (NOM departures). NOM is based on an international traveller's duration of stay, i.e. being in or out of Australia for 12 months or more, regardless of nationality, citizenship or legal status. Note that this 12-month period does not have to be continuous and is measured over a 16-month reference period.
Net interstate migration (NIM)
NIM to Victoria is the balance between the number of people moving to Victoria from other States and Territories and those moving from Victoria. Data on interstate migration cannot be directly estimated. Instead, post-censal estimates of interstate migration are modelled using administrative by-product data (for example Medicare changes of address).
Net intrastate migration
Net intrastate migration is the balance of movements of population between Victorian regions.
Implied net migration
For the smallest geographical areas, migration cannot be measured directly. The combined effects of overseas, interstate and intrastate migrations are estimated as the changes in population not explained by births or deaths.
Implied net migration = Population at end of period – population at start of period – births + deaths
Age-specific fertility rates (ASFR) are the number of live births (registered) during the calendar year, according to the age of the mother, per 1,000 women (female estimated resident population by age at the mid-point of the year 30 June). For calculating these rates, births to mothers under 15 years are included in the 15-19 years age group, and births to mothers aged 50 years and over are included in the 45-49 years age group. Pro rata adjustment is made for births for which the age of the mother is not given.
The total fertility rate (TFR) is the sum of age-specific fertility rates (live births at each age of mother per 1,000 women of that age) divided by 1,000. 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.
In VIF2019, future changes in ASFRs are modelled and the ASFR applied to the expected future female population by age to project the number of births each year. The result of the ASFR modelling is that the TFR declines from around 1.65 recently to just over 1.6 by 2036.
Mortality rates and life expectancy
Age (and sex)-specific death rates (ASDR) are the number of deaths (registered) during the calendar year, at a specified age, per 1,000 of the estimated resident population of the same age (and sex) at the mid-point of the year (30 June). Pro rata adjustment is made in respect of deaths for which the age of the deceased is not given.
Life expectancy refers to the average number of additional years a person of a given age and sex might expect to live if the age-specific death rates of the given period continued throughout his/her lifetime. While life expectancy can be expressed as years of life remaining at any age, in comparing projections it is usual to refer to life expectancy at birth.
In VIF2019, projections of ASDR are applied to the expected population to calculate the number of deaths each year. This modelling results in a life expectancy at birth of 87 years for men and 88 years for women by 2056.
In general terms, a dwelling is a structure which is intended to have people live in it, and which is habitable. Some examples of dwellings are houses, motels, flats, caravans, prisons, tents, humpies and houseboats.
Both private dwellings and non-private dwellings are counted in the Census. People in non-private dwellings (hotels, hospitals, prisons, etc.) are enumerated and counted in the population, but do not form households.
Occupied and unoccupied dwellings
Occupied and unoccupied dwellings are counted. In VIF2019, it is assumed that each occupied dwelling contains one household (it may be more than one family).
The proportion of private dwellings which are not occupied is called the Vacancy rate. In some areas, such as holiday destinations, the vacancy rate can be quite high, exceeding 50%.
The Occupancy rate is the proportion of dwellings which are occupied. By definition, Occupancy rate + Vacancy rate = 1. Victoria in Future modelling and outputs refer to the occupancy rate, as it is the occupied dwellings which accommodate the population.
A household is defined as one or more persons, at least one of whom is at least 15 years of age, usually resident in the same private dwelling. Therefore, the total number of households is equal to the total number of occupied dwellings.
Households are classified according to their composition, into the following main types:
- Couple with children
- Couple without children
- Lone parent family (with children)
- Other families of related persons household
- Lone person household
- Group household
- Others household
All these households (except the lone person households) can also include other people, related or not to the household reference person.
The term ‘child’ describes the relationship to the reference person in the family, not the age of the person. Children can be of any age.
Persons in non-private households are classified separately.
Households living arrangements and propensities
The distribution of people by age according to their position in the household is used to analyse and project household formation. This analysis has shown that the impact of the population age structure is most significant, while the effect of changes in living arrangement propensities is volatile and difficult to predict. Accordingly, in VIF2019 most of the living arrangement propensities are held constant throughout the projection period.
Average household size
The average household size is calculated as the total number of people in occupied private dwellings divided by the number of occupied private dwellings. Over the past decade, the increased proportion of small households (lone person, couple without children and one parent families) has led to a decrease in the average household size.
Australian Statistical Geographic Standard (ASGS)
VIF2019 uses the ASGS developed by the ABS. (see ABS cat. no. 1270.0).
VIF2019 publishes projections for the Greater Melbourne Capital City Statistical Area (2GMEL) and the eight Statistical Areas level 4 (SA4) in the remainder of Victoria, namely:
Warrnambool and South West.
To provide more local information, VIF2019 publishes projections for local government areas (LGA) and for a set of specifically designed small areas within each LGA. A list of these Victoria In Future Small Areas (VIFSAs) and maps are available through this link (add the link here).
For the first time in VIF2019, projections will also be published for ASGS areas as small as Statistical Area Level 2 (SA2). In built-up areas an SA2 is usually roughly equivalent to a suburb or town. In rural areas SA2s can be much larger.
The growth areas include the six LGAs of Cardinia, Casey, Hume, Melton, Whittlesea and Wyndham. When the data allows, Wallan, Beveridge and the surrounding areas (within the Shire of Mitchell) are also included.
Inner City LGAs
The Inner City LGAs are Melbourne, Port Phillip, and Yarra.
Middle Suburb LGAs
The middle suburb LGAs are: Banyule, Bayside, Boroondara, Brimbank, Darebin, Frankston, Glen Eira, Greater Dandenong, Hobsons Bay, Kingston, Knox, Manningham, Maribyrnong, Maroondah, Monash, Moonee Valley, Moreland, Mornington Peninsula, Nillumbik, Stonnington, Whitehorse, and Yarra Ranges.
Cohort Components model
The Cohort Component model projects the population by age and sex for each period using the basic demographic equation:
Population at end of period = Base population + Births – Deaths + Net migration
Housing Unit model
The Housing Unit method projects the number of dwellings available for occupation in a given area for each period using the basic equation:
Occupied dwellings at end of period =
(Base stock of dwellings + new construction – demolitions)* (1- vacancy rate)
Using an average number of persons expected in each household, the housing unit model can also be used to determine the total projected population for each area.
Household Formation model
The Household Formation model allocates the population into households, based on living arrangement propensities (i.e. the distribution of people of each age and sex across household types).
Page last updated: 12/09/19