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3101.0 - Australian Demographic Statistics, Sep 2002  
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  • How Australia Calculates the Estimated Resident Population (ERP) (Feature Article)

Feature Article - How Australia Calculates the Estimated Resident Population (ERP)


Special article published in Australian Demographic Statistics, September Quarter, 2003

The estimated resident population (ERP) is the official estimate of the population calculated by the Australian Bureau of Statistics at quarterly intervals within a year. In the Census of Population and Housing (Census) year, the ERP is first calculated at the census date, which is then backdated to calculate the ERP at 30 June of the census year. Quarterly updates are then calculated using quarterly information on births, deaths, overseas migration and interstate migration. The interstate migration is included for obtaining ERPs at the state and territory level. ERPs are used for the allocation of seats in the House of Representatives and for the distribution of funds to states and territories and lower jurisdictions.

In this article various concepts and adjustments are described which lead to the calculation of the ERP (1) at the census date, (2) at 30 June of the census year, (3) for post-censal state and territory quarterly estimates, and (4) for intercensal revision.

CENSUS COUNT

The census count is the population as enumerated in the Census in Australia. The Australian Census includes overseas visitors in Australia and excludes Australian residents overseas at the census date (7 August 2001 for the last Census). A count of Australian residents, excluding Australian residents overseas, is obtained by excluding all overseas visitors enumerated at the Census (203,100 at the 2001 Census). The census count can be tabulated by the place of enumeration (where persons are counted) and/or by the place of usual residence (where persons usually live) in Australia. It is the usual resident census count which is used in the calculation of the ERP.

UNDERENUMERATION AT THE CENSUS

The Census aims to enumerate each person present in the country on census night. However, this universal enumeration has never been possible in the censuses around the world. Some people are missed out and some are counted more than once, which usually results in a net underenumeration of the population. An adjustment for the net underenumeration of Australian residents' count at the census date is made based on the results of a Post Enumeration Survey (PES).

POST ENUMERATION SURVEY (PES)

The PES is a sample survey of households which is designed to be representative of the population of Australia. It is carried out three weeks after the census date. The aim of the survey is to enumerate a sample of households and people independently from the Census. Records of these people are then matched with census forms. People who are matched more than once, or not matched provide an estimate of people who have been counted more than once or not at all. Statistical procedures allow for the calculation of net undercount rates at the national, state and territory, and capital city/balance of state levels. Net undercount rates are also available for some subgroups of the population (Indigenous age groups, overseas born, etc).

The 2001 PES ran from 27 August to 1 September 2001. A team of 500 trained interviewers visited 37,000 households and enumerated 84,000 people. Each person, or a responsible adult responding on his/her behalf, was asked:
whether he/she was counted in the Census

  • if counted,
  • what address he/she was counted at
      • whether he/she could have been counted at other addresses (specify)
  • if not counted,
      • where he/she stayed on census night

This information was used to determine whether a person was counted, counted more than once or was not counted in the Census.

PES MATCHING AND SEARCHING

Locating the census forms corresponding to people in the PES involved two stages: matching and searching. Matching required finding an electronic image of the census form corresponding to the dwelling at which the PES interview took place while searching involved locating the census forms at the other addresses provided in the PES interview.

Once a corresponding census form image was located, the next task was to match at the person level. This was done for each PES household member and involved examining the responses common to both the PES and census forms (by name) to determine whether they were counted or missed. In most cases it was possible to identify a clear match on the basis of the name of the persons. Where the name could not be matched a judgement on whether or not a person was counted was made based on other information such as age, sex, marital status, birthplace and relationship to other members in the census household.

Further information on the 2001 PES results will be reported in Information Paper: Census of Population and Housing, Data Quality-Undercount, 2001 (cat. no. 2940.0), due for release on 1 April, 2003.

RESIDENTS TEMPORARILY OVERSEAS

ERP calculations also make an adjustment for Australian residents who happen to be temporarily absent from Australia at the census date. Using data on residents returning in the 12 months after the census date, an estimate of their numbers is made and these people are added into the population. This information is obtained from the Department of Immigration and Multicultural and Indigenous Affairs (DIMIA) using completed incoming passenger cards for Australian residents returning to Australia.

CALCULATION OF THE ERP AT THE CENSUS DATE

The PES determines the extent of net underenumeration that is required to add to the census counts on a usual residence basis. The estimate of residents temporarily overseas at the census date is then added. Further refinement of these estimates (demographic adjustments) is achieved by comparing census-based results with independent sources of population information in Australia. In particular, a demographic estimate of population by age and sex at the census date is made using yearly births, deaths and net overseas migration statistics.

CALCULATION OF THE ERP AT 30 JUNE OF THE CENSUS YEAR

The next step is to obtain ERP at 30 June of the Census year. The births, deaths and net overseas migration which occurred between 1 July and the census date (7 August for the 2001 Census) are added or subtracted from the census date ERP.

POST-CENSAL QUARTERLY STATE AND TERRITORY LEVEL POPULATION ESTIMATES

Post-censal population estimates are calculated on a quarterly basis from 30 June ERP in the Census year by updating them with the births, deaths and net overseas migration which occur in each quarter. For the state and territory level estimates, net interstate migration occurring in the quarterly periods is also included in the calculation.

INTERCENSAL REVISION OF POPULATION ESTIMATES

When the population estimates for a census year become available for the states, territories and Australia, they can be compared with the alternative estimates for the same date already produced by updating the previous census post-censal estimates. The difference between the two estimates is called the 'intercensal error'.

The Census allows an assessment of how much of the intercensal error was due to inaccuracies in estimates of interstate migration. The Census questions which allow this assessment are the questions on usual residence 1 year ago and 5 years ago. Estimates of interstate migration based on census data are used to revise the interstate migration component of the post-censal population updates (based on the previous Census). The resulting difference between the revised post-censal estimates (based on the previous Census and revised interstate migration) and the estimates based on the latest Census is a non-attributable portion, and is termed the 'intercensal discrepancy'.

The intercensal discrepancy acts as a balancing item, that when combined with births, deaths and migration equals the change in the intercensal population estimates. It is distributed on a uniform basis across quarterly population estimates in the intercensal period.
INTERCENSAL DISCREPANCY, 1996-2001

Intercensal discrepancy

'000
%

New South Wales
21.4
0.33
Victoria
-26.9
-0.56
Queensland
-3.9
-0.11
South Australia
2.7
0.18
Western Australia
-5.1
-0.27
Tasmania
0.1
0.01
Northern Territory
0.3
0.15
Australian Capital Territory
1.3
0.42
Australia(a)
-10.6
-0.05

(a) Includes Other Territories comprising Jervis Bay Territory, Christmas Island and the Cocos (Keeling) Islands.

For more information, please see Demographic Estimates and Projections: Concepts, Sources and Methods, in the Statistical Concepts Library on this site.


COMPONENTS OF ESTIMATED RESIDENT POPULATION, 30 June 2001(a)

New
Australian
South
South
Western
Northern
Capital
At end of period
Wales
Victoria
Queensland
Australia
Australia
Tasmania
Territory
Territory
Australia(b)

'000
'000
'000
'000
'000
'000
'000
'000
'000

MALES
Components as at
7 August, 2001-
Census count,
actual location
3,145.4
2,279.1
1,803.8
722.3
922.3
224.0
110.2
153.4
9,362.0
Plus residents
absent interstate
36.1
41.2
17.1
12.8
8.9
4.9
2.1
5.2
128.5
Less interstate
visitors
29.1
16.8
47.3
7.1
10.5
2.2
10.4
4.9
128.5
Less overseas
visitors
28.7
15.6
32.2
3.8
9.0
0.9
4.0
1.3
95.5
Equals census
count, place of
usual residence
3,123.7
2,287.9
1,741.5
724.1
911.7
225.9
97.9
152.5
9,266.5
Plus allowance
for under-
enumeration(c)
79.3
39.6
44.3
14.4
21.1
4.7
4.3
2.0
209.7
Plus residents
temporarily
overseas
66.3
43.7
24.3
9.2
20.2
1.9
1.3
3.3
170.2
Equals ERP as at
7 August 2001
3,269.3
2,371.2
1,810.1
747.7
953.0
232.5
103.6
157.7
9,646.5
Components from
1 July to
7 August 2001-
Less births
4.4
3.2
2.5
0.9
1.3
0.3
0.2
0.2
13.0
Plus deaths
2.7
1.8
1.4
0.7
0.7
0.2
0.1
0.1
7.7
Less net inter-
state migration
-0.6
0.4
0.9
-0.1
-0.2
-0.1
-0.1
-0.1
. .
Less net per-
manent and long-
term overseas
movement
4.0
3.2
1.7
0.3
1.1
0.1
-
0.2
10.6
Less category
jumping
-
-
-
-
-
-
-
-
-
Equals ERP as at
30 June 2001
3,264.2
2,366.3
1,806.4
747.3
951.6
232.5
103.5
157.6
9,630.7

FEMALES
Components as at
7 August, 2001-
Census count,
actual location
3,226.3
2,365.9
1,851.3
744.9
929.0
232.6
100.5
158.6
9,610.3
Plus residents
absent interstate
31.7
37.9
13.5
11.2
6.9
5.0
1.7
4.6
112.5
Less interstate
visitors
23.2
13.4
47.0
5.7
9.0
1.9
8.1
4.2
112.5
Less overseas
visitors
31.9
17.3
37.3
4.5
10.3
1.0
3.9
1.4
107.6
Equals census
count, place of
usual residence
3,202.9
2,373.0
1,780.6
745.9
916.6
234.8
90.2
157.5
9,502.7
Plus allowance
for under-
enumeration(c)
50.9
27.7
24.2
9.9
16.5
2.7
3.2
1.3
136.4
Plus residents
temporarily
overseas
62.1
42.4
22.2
9.1
18.2
1.8
1.0
3.1
160.0
Equals ERP as at
7 August 2001
3,315.9
2,443.2
1,827.0
764.9
951.4
239.4
94.3
161.9
9,799.1
Components from
1 July to
7 August 2001-
Less births
4.1
3.0
2.4
0.9
1.2
0.3
0.2
0.2
12.4
Plus deaths
2.6
1.8
1.2
0.7
0.6
0.2
-
0.1
7.1
Less net inter-
state migration
-0.9
0.3
1.2
-0.2
-0.1
-0.1
-0.2
-0.1
. .
Less net per-
manent and long-
term overseas
movement
4.2
3.1
2.1
0.4
1.3
-
-
0.1
11.3
Less category
jumping
-
-
-
-
-
-
-
-
-
Equals ERP as at
30 June 2001
3,311.0
2,438.4
1,822.5
764.5
949.6
239.3
94.3
161.7
9,782.6

PERSONS
Components as at
7 August, 2001-
Census count,
actual location
6,371.7
4,645.0
3,655.1
1,467.3
1,851.3
456.7
210.7
311.9
18,972.4
Plus residents
absent interstate
67.8
79.1
30.7
24.0
15.8
9.9
3.9
9.8
241.0
Less interstate
visitors
52.4
30.2
94.3
12.9
19.5
4.1
18.5
9.0
241.0
Less overseas
visitors
60.6
32.9
69.5
8.3
19.2
1.8
7.9
2.8
203.1
Equals census
count, place of
usual residence
6,326.6
4,661.0
3,522.0
1,470.1
1,828.3
460.7
188.1
310.0
18,769.2
Plus allowance
for under-
enumeration(c)
130.2
67.3
68.5
24.3
37.6
7.4
7.5
3.3
346.2
Plus residents
temporarily
overseas
128.4
86.1
46.5
18.3
38.5
3.7
2.3
6.4
330.2
Equals ERP as at
7 August 2001
6,585.2
4,814.4
3,637.1
1,512.6
1,904.4
471.8
197.9
319.7
19,445.6
Components from
1 July to
7 August 2001-
Less births
8.6
6.2
4.9
1.8
2.5
0.5
0.4
0.4
25.4
Plus deaths
5.3
3.6
2.6
1.4
1.3
0.4
0.1
0.2
14.8
Less net inter-
state migration
-1.6
0.7
2.1
-0.3
-0.3
-0.2
-0.2
-0.2
. .
Less net per-
manent and long-
term overseas
movement
8.2
6.4
3.7
0.7
2.4
0.1
-
0.3
21.8
Less category
jumping
-
-
-
-
-
-
-
-
-
Equals ERP as at
30 June 2001
6,575.2
4,804.7
3,628.9
1,511.7
1,901.2
471.8
197.8
319.3
19,413.2

. . not applicable
- nil or rounded to zero (including null cells)
(a) Final estimates.
(b) Includes Other Territories.
(c) On a usual residence basis.


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