SCOPE AND COVERAGE
1 The 2001 Census of Population and Housing was held on 7 August 2001. Australia's first national Census was held in 1911 and since 1961 a census has been taken every five years, a frequency which is specified in the Census and Statistics Act 1905. The objective of the Census is to count the number of people in Australia on Census Night, identifying their key characteristics and those of the dwellings in which they live.
2 The Census aims to count every person who spent Census Night in Australia. This includes Australian residents in Antarctica and people in the territories of Jervis Bay, Cocos (Keeling) Islands and Christmas Island. The other Australian External Territories, Norfolk Island and minor islands such as Heard and McDonald Islands, are outside the scope of the Australian Census. The only people in Australia on Census Night who are excluded from the Census are foreign diplomats and their families.
3 The Census includes people on vessels in or between Australian ports, on board long distance trains, buses or aircraft and on oil or gas rigs off the Australian coast. People entering Australia before midnight on Census Night are counted while people leaving an Australian port for an overseas destination before midnight on Census Night are not. Visitors to Australia are included regardless of how long they have been in the country or how long they plan to stay. However, for people who intend to be in Australia less than one year, only basic demographic data are available. The Census includes homeless people and people camping out.
4 All occupied dwellings are counted in the Census with the exception of diplomatic dwellings. Unoccupied private dwellings are also counted with the exception of unoccupied dwellings in caravan parks, marinas and manufactured home estates, and units in accommodation for the retired or aged (self-care). Unoccupied residences of owners, managers or caretakers of such establishments are counted.
5 Details about the 2001 Census content, collection operations, confidentiality and privacy protection, processing and evaluation activities are contained in 2001 Census of Population and Housing: Nature and Content (cat. no. 2008.0).
ABS POPULATION ESTIMATES
6 All counts in this publication are on a 'place of enumeration' basis. 'Place of enumeration' means where the person was counted on Census Night. The Census can provide person counts based on 'place of usual residence' for Collection Districts (CDs) and aggregations of CDs. Appendix 1-Estimated Resident Population highlights the difference between these two measures.
7 The Estimated Resident Population (ERP) is the official Australian Bureau of Statistics (ABS) estimate of the Australian population. The ERP is based on results of the Census of Population and Housing. It is compiled as at 30 June of each census year and updated quarterly between censuses. The intercensal estimates of the resident population are revised following the next census.
8 The ERP is derived from census usual residence counts, by making the following three important adjustments:
- An adjustment for census net under enumeration (or under count). The level of under enumeration is derived from the Post Enumeration Survey which is conducted soon after the Census, and from estimates based on demographic analysis.
- The inclusion of an estimated number of Australian residents who are temporarily overseas on Census Night and are therefore not covered by the Australian Census. The number of such people is estimated from statistics on overseas arrivals and departures.
9 ABS population estimates are published in Australian Demographic Statistics (cat. no. 3101.0), produced quarterly, and in Population by Age and Sex, Australian States and Territories (cat. no. 3201.0) produced annually. ERPs for Statistical Local Areas (SLAs) are published in Regional Population Growth, Australia and New Zealand (cat. no. 3218.0).
10 The ABS also provides projections (based on different assumptions as to future fertility, mortality and migration) of the resident population of Australia, states and territories. These projections are published every two years in Population Projections, Australia (cat.no.3222.0).
11 Census data are subject to a number of inaccuracies resulting from errors by respondents or mistakes in collection or processing. Whilst many of these are corrected by careful processing procedures, some still remain. The effect of the remaining errors is generally slight, although it may be more important for small groups in the population. The main kinds of error to keep in mind are:
- The third adjustment occurs because the Census does not fall on 30 June. For example, the 2001 Census was held on 7 August. Back dating of population estimates from 7 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 7 August.
- Partial non-response: In some cases where an answer is not provided to a question, an answer is imputed (often from other information on the form). In other cases a 'Not stated' code is allocated.
- Processing error: While such errors can occur in any processing system, quality management is used continuously to improve the quality of processed data, and to identify and correct data of unacceptable quality.
- Random adjustment: Table cells containing small values are randomly adjusted or suppressed to avoid releasing information about particular individuals, families, or households. The effects of these adjustments are statistically insignificant.
- Respondent error: Because processing procedures cannot detect or repair all errors made by people in completing the forms, some remain in final data.
12 Further information on data quality is provided progressively in Census Update and in 2001 Census Papers.
QUALITY OF INDIGENOUS STATISTICS
13 For further information on the quality of Indigenous statistics, see Population Distribution, Aboriginal and Torres Strait Islander Australians (cat. no. 4705.0). This publication presents counts for Aboriginal and Torres Strait Islander Australians from the 2001 Census for Indigenous geographic areas, accompanied by information on data quality to help interpret the data. Estimates of the Indigenous population, based on the 2001 Census, are also included. For comprehensive information on the quality of Indigenous census data, see Population Issues, Aboriginal and Torres Strait Islander Australians (cat. no. 4708.0).
14 Overseas visitors are defined differently for the 2001 Census. For the 1996 Census overseas visitors were defined as any person who stated they would be in Australia for less than 6 months. For the 2001 Census they are defined as any person who stated they would be in Australia for less than 12 months. Data for overseas visitors are restricted to age, sex and marital status.
CALCULATION OF PROPORTIONS
15 When calculating the proportion of the population with a particular characteristic, 'Not stated' responses are included in the denominator. For example, in the Summary of findings, the proportion of people who are of Indigenous origin is calculated by dividing the number of persons who stated that they were of Indigenous origin by the total population and expressing the result as a percentage. The total population includes the category 'Not stated'.
16 For census variables which include data for overseas visitors i.e. age, sex and marital status, the category 'Overseas visitor' is also included in the denominator.
CALCULATION OF MEDIANS
17 A median is a measure of central tendency. It is a mid value which divides a population distribution into two, with half the observations falling below it and half above it. Unlike averages (means) medians are not usually skewed by extreme observations.
18 There are a number of issues to be aware of:
- Under count: Although the Census aims to count each person, there are some people who are missed and others who are counted more than once. The data in this publication are not adjusted for the net under count.
- The categories 'Not stated' and 'Not applicable' are not included in the calculation of medians.
- The category 'Overseas visitor', is only included in the calculation of the median when data for overseas visitors is collected for the variable (see paragraph 14). For example, 'Median age' (table 1) includes overseas visitors whereas 'Median weekly individual income' (also in table 1) does not.
- If a median falls into a category that has a text-only label, then a value of '0' is used for that category. For this publication this is only relevant to the calculation of 'Median weekly individual income' (table 1), as the income classification (mnemonic INCP) includes categories 'Nil income' and 'Negative income'.
- When calculating a median on a classification containing ranges, the median may fall into a range which is open-ended. In this case, the median would be set to the number in the range's label. For example, in the calculation of 'Median weekly individual income', if the median was to fall in the last range $1,500 or more, then $1,500 would be allocated as the median.
19 The 1996 Census dollar values for 'Median weekly individual income' (table1), 'Median monthly loan repayment' (table 6) and 'Median weekly rent' (table 6) have not been adjusted into 2001 dollars.
The following abbreviations have been used in this publication.
- 'Median monthly loan repayment' and 'Median weekly rent' (both in table 6) are based on the ranged variables HLRD01 and RNTD01 respectively (see Glossary). This is due to difficulties associated with the large number of small cells when using individual dollar values to perform these calculations. An adjustment has been made to HLRD01, with the range $1,500 and over changed to $1,500-$1,999 and an additional range $2,000 and over added.
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