Population Projections, Australia methodology

Under a '12/16 month rule', incoming overseas travellers (who are not currently counted in the population) must be resident in Australia for a total period of 12 months or more, during the 16 month follow-up period to then be added to the estimated resident population. Similarly, those travellers departing Australia (who are currently counted in the population) must be absent from Australia for a total of 12 months or more during the 16 month follow-up period to then be subtracted from the estimated resident population.

The 12/16 month rule does not have to be continuous and takes account of those persons who may have left Australia briefly and returned, while still being resident for 12 months out of 16. Similarly, it takes account of Australians who live most of the time overseas but periodically return to Australia for short periods.

The ASGS brings all the regions for which the ABS publishes statistics within the one framework and has been in use for the collection and dissemination of geographically classified statistics since 1 July 2011. It is the current framework for understanding and interpreting the geographical context of statistics published by the ABS. For further information see Australian Statistical Geography Standard (ASGS): Volume 1 - Main Structure and Greater Statistical Areas (cat. no. 1270.0.55.001).

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 divided by the number of people aged 15-64 years, multiplied by 100.

Age-specific death rates are the number of deaths (on either an occurred or registered basis) during the calendar year at a specified age per 1,000 of the estimated resident population of the same age at 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.

Age-specific fertility rates are the number of live births occurring during the calendar year, according to the age of the mother, per 1,000 of the female estimated resident population of the same age at 30 June. For calculating these rates, births to mothers under 15 years are included in the 15 year–old age group, and births to mothers aged 50 years and over are included in the 49 year–old age group.

Refers to people born Post-World War II between the years 1946 and 1964.

The delivery of a child, irrespective of the duration of pregnancy, who, after being born, breathes or shows any evidence of life such as a heartbeat.

Refers to the Greater Capital City Statistical Areas of states and territories as defined in the Australian Statistical Geography Standard.

The complete enumeration of a population at a point in time with respect to well-defined characteristics (e.g. Persons, Manufacturing, etc.). When the word is capitalised, "Census" refers to the national Census of Population and Housing.

Death is the permanent disappearance of all evidence of life after birth has taken place. The definition excludes deaths prior to live birth.

For the purposes of the Deaths and Causes of Death collections compiled by the ABS, a death refers to any death which occurs in, or en route to Australia and is registered with a state or territory Registry of Births, Deaths and Marriages.

Based on the rate of change in population over a period (expressed as a percentage). See population growth rate.

Represent the socioeconomic area of each of the eight state and territory capital cities. These boundaries are built from aggregations of whole Statistical Areas Level 4. GCCSA boundaries represent a broad socioeconomic definition of each capital city, they contain not only the urban area of the capital city, but also surrounding and non-urban areas where much of the population has strong links to the capital city, through for example, commuting to work. For further information see Australian Statistical Geography Standard (ASGS): Volume 1 - Main Structure and Greater Statistical Areas (cat. no. 1270.0.55.001).

The movement of people over a state or territory boundary for the purpose of changing their place of usual residence. Net interstate migration is the difference between arrivals and departures and can be either positive or negative.

Based on absolute change in population over a period.

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 or her lifetime.

A life table is a statistical model used to represent the mortality experience of a population. In its simplest form, a life table is generated from age-specific death rates and the resulting values are used to measure mortality, survivorship and life expectancy. The life table functions relevant to population projections are:

• qx - the proportion of persons dying between exact age x and exact age x+1. It is the mortality rate, from which other functions of the life table are derived; and
• ex - life expectancy at age x.
   

For any distribution, the median value is that which divides the relevant population into two equal parts, half falling below the value, and half exceeding it. Thus, the median age is the age at which half the population is older and half is younger.

The number of births minus the number of deaths.

Overseas migration is the movement of people in and out of Australia for the purpose of changing their country of usual residence. Overseas migrant arrivals are incoming travellers who are not currently counted in the population and who stay in Australia for 12 months or more over a 16-month period, and are then added to the population. Overseas migrant departures are outgoing travellers who are currently counted in the population and who leave Australia for 12 months or more over a 16-month period, and are then subtracted from the population. Net overseas migration is the difference between arrivals and departures and can be either positive or negative.

For Australia, population growth is the sum of natural increase and net overseas migration. For states and territories, population growth also includes net interstate migration.

Population change over a period as a proportion (percentage) of the population at the beginning of the period.

The ABS uses the cohort-component method for producing population projections of Australia, the states, territories, capital cities and balances of state. This method begins with a base population for each sex by single year of age and advances it year by year, for each year in the projection period, by applying assumptions regarding future fertility, mortality and migration. The assumptions are based on demographic trends over the past decade and longer, both in Australia and internationally. The projections are not predictions or forecasts, but are simply illustrations of the change in population which would occur if the assumptions were to prevail over the projection period. A number of projections are produced by the ABS to show a range of possible future outcomes.

Replacement level fertility is the number of babies a female would need to have over her reproductive life span to replace herself and her partner. Given the current mortality of females up to age 49 years, replacement fertility is estimated at 2.1 babies per female.

Within each state and territory, except for the ACT, the area not defined as being part of the Greater Capital City Statistical Area is called the Rest of state region.

The sex ratio relates to the number of males per 100 females. The sex ratio is defined for total population, at birth, at death and among age groups by appropriately selecting the numerator and denominator of the ratio.

Standardised death rates (SDR) enable the comparison of death rates between populations with different age structures by relating them to a standard population. The current standard population is all persons in the Australian population at 30 June 2001 (19,413,240), as published prior to recasting the ERP series. SDRs are expressed per 1,000 or 100,000 persons. There are two methods of calculating SDRs:

• The direct method - this is used when the populations under study are large and the age-specific death rates are reliable. It is the overall death rate that would have prevailed in the standard population if it had experienced at each age the death rates of the population under study; and
• The indirect method - this is used when the populations under study are small and the age-specific death rates are unreliable or not known. It is an adjustment to the crude death rate of the standard population to account for the variation between the actual number of deaths in the population under study and the number of deaths which would have occurred if the population under study had experienced the age-specific death rates of the standard population.
   

State or territory of usual residence refers to the state or territory of usual residence of:

• the population (estimated resident population);
• the mother (birth collection); and
• the deceased (death collection).

In the case of overseas movements, state or territory of usual residence refers to the state or territory regarded by the traveller as the one in which he/she lives or has lived. State or territory of intended residence is derived from the intended address given by overseas arrivals, and by Australian residents returning after a journey abroad. Particularly in the case of the former, this is not necessarily the state or territory in which the traveller will eventually establish a permanent residence.

The sum of age-specific fertility rates (live births at each age of mother per female population 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 (ages 15-49).

Usual residence within Australia refers to that address at which the person has lived or intends to live for a total of six months or more in a given reference year.

ABS population projections are based on a series of assumptions on future levels of fertility, mortality, net overseas migration and net interstate migration. Assumptions are derived from an analysis of data sourced from a variety of institutional environments. Much of this data is administrative by-product data collected by other organisations. Assumptions on fertility and mortality are based on births and deaths statistics extracted from registers administered by the various States and Territory Registrars of Births, Deaths and Marriages. Passenger card data and related information provided to the Department of Home Affairs provides information on overseas migration to/from Australia, which is then used to make assumptions about future levels of net overseas migration. Medicare Australia client address data is used to estimate interstate migration, from which assumptions on future levels of net interstate migration are derived.

ABS Census of Population and Housing and Post Enumeration Survey (PES) data are used to determine a base population from which estimated resident population (ERP) is calculated. The ERP for the latest available year is used as the base population for the population projections. For information on the institutional environment of the Australian Bureau of Statistics (ABS), please see ABS Institutional Environment.

Population projections inform on future changes in the population of Australia, such as population growth/decline and changes in age structure, and are therefore used in a variety of key planning decisions. Projections are published for the states, territories, capital cities and rest of states, by single year of age and sex. Projected numbers of births and deaths are published.

Assumptions on future levels of fertility, mortality, net overseas migration and net interstate migration are formulated on the basis of demographic trends over the past decade and longer, both in Australia and overseas, in conjunction with consultation with various individuals and government department representatives at the national and state/territory level.

ABS population projections are compiled and published once in each five year period; typically, two to three years following the most recent ABS Census of Population and Housing.

ABS population projections are based on a number of assumptions on future levels of fertility, mortality, net overseas migration and net interstate migration. They are not intended as predictions or forecasts, but are illustrations of growth and change in the population that would occur if the assumptions were to prevail over the projection period.

While the assumptions are formulated on the basis of an assessment of past demographic trends, both in Australia and overseas, there is no certainty that any of the assumptions will be realised. In addition, the assumptions do not attempt to allow for non-demographic factors (such as major government policy decisions, economic factors, catastrophes, wars, epidemics or significant health treatment improvements) which may affect future demographic behaviour or outcomes.

Data used in the formulation of the assumptions are subject to non-sampling error. For more information on the accuracy of these component data collections see Quality Declaration Summary - Australian Demographic Statistics (cat. no. 3101.0).

As the assumptions used in each successive set of population projections incorporate recent trends, comparison of data across issues of this publication is not possible.

ABS population projections are not intended as predictions or forecasts, and should not be considered as such. Rather, they are illustrations of growth and change in the population that would occur if the assumptions were to prevail over the projection period. As future levels of fertility, mortality, overseas migration and internal migration are unpredictable, two or more assumptions have been made for each component. These are intended to illustrate a range of possible future scenarios.

For more information on the method used to compile ABS population projections see Demographic Estimates and Projections: Concepts, Sources and Methods (cat. no. 3228.0) and Chapter 2—Assumptions of Population Projections, Australia (cat. no. 3222.0).

ABS population projections are available in a variety of formats on the ABS web site under the 3222.0 product family. The formats available are:

• Main Features, which contains key figures commentary;
• Time Series Spreadsheets for Australia and the states and territories, by single year of age and sex, for the 3 selected projection series (Series A, B and C);
• Data cubes (in ABS.Stat format) containing population projections for Australia, the states, territories, capital cities and rest of state, by single year of age and sex, for all projection series; and
• Two data cubes (in Microsoft Excel format). The first data cube contains population projections, components of change and summary statistics for Australia, the states, territories, capital cities and rest of state, for the three selected projection series (Series A, B and C). The second data cube contains projection assumptions.
   

If the information you require is not available as a standard product, then ABS Consultancy Services can help you with customised services to suit your needs. For inquiries contact the National Information and Referral Service on 1300 135 070 or email client.services@abs.gov.au.