POPULATION MEASURES

Australia's population can be measured in several ways:

• Census counts by place of enumeration;

• Census counts by place of usual residence; and

• estimated resident population.

In addition, the Census provides counts of:

• the working population; and

• families and households.

CENSUS COUNTS - PLACE OF ENUMERATION

The Census count for place of enumeration is a count of every person in Australia on Census Night, based on where they were located on that night. This may or may not be the place at which they usually reside.

It includes:

• people on board vessels in or between Australian ports, or on long-distance trains, buses or aircraft;

• people entering Australia from overseas before midnight on Census Night; and

• Australian residents in Antarctica.

It excludes:

• people leaving an Australian port for an overseas destination before midnight on Census Night;

• Australian residents out of the country on Census Night; and

• overseas diplomatic personnel and their families in Australia.

Visitors to Australia are counted regardless of how long they have been in the country or how long they plan to stay. In the 1996 Census, overseas visitors were those people who indicated they would be usually resident in Australia for less than six months. For the 2001 Census, this was changed to less than one year. For the 2006 Census, overseas visitors are again those people who indicated they would be usually resident in Australia for less than one year. Data on overseas visitors is only available for three variables: Age (AGEP), Sex (SEXP) and Marital Status (MSTP). A special 'Overseas visitor' category has been created for all other person variables.

The Census count by place of enumeration provides a snapshot in any given area. Although the Census is timed to attempt to capture the typical situation, the large number of visitors to holiday resort areas, such as the Gold Coast and snow fields, may result in a high enumeration count compared with the usual residence count.

Census counts based on place of enumeration can be provided for individual Collection Districts (CDs), and any aggregations of CDs, such as postal areas or Statistical Local Areas (SLAs).


CENSUS COUNTS - PLACE OF USUAL RESIDENCE

The Census count for Place of Usual Residence is a count of every person in Australia on Census Night, based on the area in which they usually live. Each person is required to state his/her address of usual residence on the census form. Where sufficient information is provided, this enables the area in which they usually reside to be identified and coded.

Census counts compiled on this basis minimise seasonal factors such as the school holidays and snow season, and provide information about the usual residents of an area.

The 2001 Census was the first census where usual residence data for Census Night was available at CD level. Previously, Place of Usual Residence was only coded to SLA level. Where respondents gave insufficient address information, their SLA was imputed as in the past. Their CD however, was not imputed in these cases for 2001, but instead was classified as 'Inadequately described'.

For the 2006 Census, usual residence data will again be available at CD level. If respondents give insufficient usual address information, their usual residence is imputed at CD level.


ESTIMATED RESIDENT POPULATION

The Estimated Resident Population (ERP) is the official ABS estimate of the Australian population. Among its many uses are the determination of the number of representatives from each state (and territory) to sit in the House of Representatives, and the annual allocation of Commonwealth funds for state governments and local government. The ERP is based on Census of Population and Housing usual residence counts. It is compiled as at 30 June of each census year and updated quarterly between censuses. These intercensal estimates of the resident population are revised each time a population census is conducted.

In compiling 30 June ERP for a census year, three important factors are taken into account:

• Census net underenumeration (or undercount). The level of underenumeration is derived from the Census Post Enumeration Survey which is conducted soon after the Census, and from estimates based on demographic analysis.

• Australian residents who are temporarily overseas on Census Night and are therefore not covered by the Australian Census. The number of such people is obtained from statistics on overseas arrivals and departures.

• The Census does not fall on 30 June. For example, the 2006 Census was held on 8 August. Back-dating of population estimates from 8 August to 30 June is accomplished using data from birth and death registrations, overseas arrivals and departures, and estimates of interstate migration, for the period 1 July to 8 August.

THE WORKING POPULATION

The working population consists of all persons who were employed in the week prior to Census Night. It is not possible to distinguish between workers working standard hours and shift workers, as the data collected relate to all workers.

The working population can be used to calculate daytime populations for an area. These are particularly relevant in commercial and industrial areas. These data, when combined with statistics on how people get to work and on the availability of cars, are used to plan for roads and public transport. They are also used in planning for the location of services, since many services need to be located where people will be during the day, rather than where they live.


FAMILIES AND HOUSEHOLDS

Family and household data from the Census are based on persons usually resident. When coding the variables Family Composition (FMCF) and Household Composition (HHCD), information about usual residents temporarily absent is taken into account and visitors to the household are disregarded.

Age, sex, student status and relationship information are collected for persons temporarily absent, as this is sufficient for family and household coding purposes. All other information for persons temporarily absent, and in Australia on Census Night, should have been obtained at their place of enumeration. However, this information is not able to be related back to their place of usual residence.

Coders use the following temporary absentees in determining household and family classifications:

• partners,

• children; and

• co-tenants or unrelated flatmates (used to classify group households).

Note that family and household structures are not coded for dwellings where all occupants are absent on Census Night, for example, on holidays. The dwelling would be classified as unoccupied and the holidaying family would be coded as a visitor only household at the holiday home.