The Census of Population and Housing is the most extensive statistical collection undertaken by the Australian Bureau of Statistics (ABS). It collects a variety of social and demographic information from all members of the community.

The results of the census are used by government, industry, academics, many other sectors of the community and private individuals for planning and decision making activities that can affect the lives and welfare of all Australians. Census statistics are used in researching many social problems and as a basis for planning by industry and commerce within the community. Census data also provide an essential basis for the preparation of population estimates at the national, State and local government levels.

Census-taking in Australia

Population counts have been conducted from a very early period in Australia's history. Initially, these counts were solely head counts celled 'musters', which were important as a means of matching food and other supplies to the numbers of people needing them. The first regular census was taken in New South Wales in 1828 using census-taking methods essentially adapted from methods used in England at that time.

With Federation in 1901, census-taking became the responsibility of the Commonwealth Government. In 1905 the Census and Statistics Act was passed which gave authority to the Governor-General to appoint a Commonwealth Statistician, one of whose duties was the taking of the census.

The Census and Statistics Act 1905 stipulated that a census was to be taken in 1911 and every tenth year thereafter. The Act also stipulated a number of topics which must be asked in each census: name; age; sex; relationship; marital status; duration of marriage; birthplace; nationality; period of residence; religion; occupation; material of outer walls and number of rooms in the dwellings; and allowed for other topics to be included 'as prescribed'. Since 1911 censuses have been held in 1921, 1933, 1947, 1954, 1961, 1966 and 1971.

In 1930 the Act was amended to make the year in which the census was to be conducted more flexible. The Act, which had stated that a census be taken in every tenth year, was amended by the addition of the words 'or at such other times as prescribed'.

Since 1961 a census has been held every five years because of the need to collect, more frequently, data that can only be produced by complete enumeration.

Census collection

The Census and Statistics Act 1905 specifies the manner in which the census must be collected. Section 10(1) states that 'For the purpose of taking the census, a form called the Householder's Schedule shall be prepared, and left, in accordance with the regulations, at every dwelling throughout the Commonwealth'. The distribution of the census schedule to each household prior to census day and the collection after census day is undertaken by specially trained census collectors.

The census field operation is controlled and conducted jointly by the Australian Bureau of Statistics and the Australian Electoral Office. Permanently employed Divisional Returning Officers in the Electoral Office become Divisional Field Supervisors for the census and they are responsible for the recruitment, training and general supervision of temporary census staff. Approximately 2500 group leaders and 30,000 collectors are recruited for short term duties. Each group leader is responsible for approximately 12 collectors who themselves are responsible for the delivery and collection of census forms from an average of 200 dwellings.

The special collectors recruited to deliver and collect the forms in large establishments (hospitals, hotels, gaols, etc.) are usually the proprietors or managers of individual establishments. Likewise, the persons in charge of trains, buses, planes etc. in transit on census night are usually recruited as special collectors for the enumeration of persons travelling throughout census night.

Every effort is made to avoid having collectors work in the same area as they live to avoid, as far as possible, the collection of information from people they know personally. Aboriginal collectors are used in areas where there is a large Aboriginal population. All staff employed either temporarily or permanently on the census sign an undertaking which provides that he/she will not, without lawful authority, alter any document or form and will not divulge the contents of any form filled up or information obtained in the course of his/her duties.

The Australian census uses a self-enumeration approach to obtain information i.e. each household fills in the details required on the census schedule on its own behalf. This method of collecting information determines the type of questions which can feasibly be included on the census schedule. Topics which involve canvassing opinion, rely heavily on memory, require a large number of questions or an excessive amount of explanation are considered unsuitable for a self-enumeration census.

In the census, all members of the community are counted at the dwelling in which they are staying on census night, regardless of where they usually live. Special provision is made for persons who are not in a private or non-private dwelling, e.g. camping out, at work, travelling on long distance trains or buses and those on boats or planes. The census does not count Australian residents who are overseas but does count people who are visiting Australia. Diplomatic representatives, their families and their dwellings are excluded.

Wednesday 30 June 1976 was proclaimed as census night.

Census processing sequences

Answers given to census questions have to be converted to a form in which they can be read into a computer. In some cases this involves coding information such as family relationship, labour force status and industry of employment, before it can be transferred to magnetic tape or disc. A number of edits (tests) aimed at detecting and adjusting for some common types of error and some other control processes (both described in detail below) are also carried out to complete processing.

Processing of the 1976 census was conducted in two phases. Preliminary processing conducted soon after Census night produced a complete count of the population classified by age, sex, marital status and birthplace (Australia, UK and Other). Subsequent processing was deferred until 1977-78 as a result of government expenditure cuts.

However, before the commencement of the final processing phase further budgetary restrictions were imposed and in order to meet these constraints as well as processing all topics included on the schedule to satisfy users' demands, it was decided to process only a sample of schedules in the final processing phase.

The following sampling scheme was adopted:

(a) Process all schedules from non-private dwellings (motels, hostels, gaols etc. - see Section 4) in Australia

(b) Process all schedules from private dwellings in the Northern Territory

(c) Process 50% of schedules from private dwellings in all other States and the ACT. This sample was selected at the Collection District (CD) level by randomly selecting either the first or second private dwelling in the CD, and then systematically taking every second private dwelling after that. All persons within each selected dwelling were included in the sample.

In determining the best sampling scheme to be used for selecting schedules for the final processing, consideration was given to

(a) The need to provide sufficiently accurate estimates of different types of people (hence the decision to process all schedules from non-private dwellings and the Northern Territory).

(b) The ease with which the sample could be manually selected during processing (hence the decision to include 50% of all schedules from private dwellings).

The huge sample size (in excess of 6.5 million persons) used to derive figures for the 1976 Census ensures an adequate representation of all components of the Australian population and guarantees the production of reliable estimates for the many minority groups of interest to users.

It is important to note that a 50% sample of the private dwellings in a CD may not contain 50% of the people who live in all private dwellings of that CD (as counted in the preliminary processing phase). In addition the efficiency of the sample design can be improved by taking advantage of the complete counts obtained from the preliminary processing phase which included all schedules. Therefore counts of persons obtained from the 50% sample are not multiplied by 2 to get CD estimates, but by a different factor (usually very close to 2) which ensures that the totals for males, females and all persons, derived from the final processing phase, agree with those from the preliminary processing phase. Final counts of private dwellings are obtained by multiplying the number selected in each CD by 2. The calculated private dwelling figure can then be added to the number of non-private dwellings in the CD to get total dwellings in the CD.

Editing and associated procedures

The aim of editing during census processing is to reduce the number of errors in the data. The kind of errors that editing procedures can detect are limited to answers which are inconsistent or invalid. No correction is possible for errors which do not show up in this way.

In the processing of the 1976 Census there was no correction without reference to source documents for items which failed edits. Imputation of missing data was made in respect of only five items age, sex, marital status, birthplace and occupational status and then only when there was sound basis for such action. These are items frequently used in tabulations. (check this paragraph)

Two broad types of edits were applied to 1976 Census processing:

(a) Balancing edits were employed to ensure that the total numbers of persons and dwellings in each CD remained consistent at all stages of processing.

(b) Consistency edits were designed to detect responses which appeared to be inconsistent with other responses on the same schedule, or in conflict with census definitions or processing rules.

Apparent inconsistencies in the transcribed census schedule records could result from errors by the respondent in completing the schedule, or by errors in coding or transcribing the information onto magnetic tape or disc. Edits were applied to detect such cases as those in which a person was shown as aged less than 15 years and was also shown as having a marital status other than never married; or when stated age less stated duration of marriage indicated an age of less than 15 years. Although the number of edit failures due to respondent error was small, there were cases when, because of the absence of conclusive information, subsequent adjustment of records was necessarily somewhat arbitrary.

In processing the information from census schedules, all data items are fed into the computer in the form of codes. Edits which test processing rules are applied to ensure that these codes fall into the permitted range. For example, the broken sequence of numbers allocated for occupation codes does not include numbers in the range 092-099; any occupation coding in this range would fail the edit and re-coding would be necessary.

Sources of error in the census

In an operation the size of the census there are many ways for errors to find their way into the final results. As in other areas of statistics, considerable effort is directed to devising procedures to ensure the highest possible level of accuracy consistent with constraints of cost and burden on respondents. While it is clearly not possible to eliminate all inaccuracies, and some errors will survive in the final results, it is unlikely that remaining errors would have any significance in aggregated census data.

Figures derived from the 1976 Census are subject to two types of errors.

Sampling errors. Since the Census figures derived from final processing are based on a 50% sample of schedules, it is likely that they will differ from the figures that would have been obtained if all schedules had been processed. These differences are called sampling errors. Measures of sampling errors have been calculated and are presented together with a more detailed explanation in Section 4.

Non-sampling errors. These are the errors that would have been present even if all schedules had been processed, thus their occurrence in no way depends on the sampling of census schedules for processing. Major types of non sampling errors are:

(a) Under-enumeration

The census aims at counting every person and dwelling (excluding diplomatic personnel and their residences) in Australia on census night. While every effort is made to minimise undercounting in the census, some inevitably occurs - for example, the inadvertent omission of very young children or the treatment by the census collector of an occupied dwelling as unoccupied. Refusal by householders to complete the census schedule is not a significant cause of under-enumeration and accounts for less than 0.5% of households. In about 70% of these cases the number of occupants was able to be estimated by the collector from information obtained orally from a member of the household or other persons and this estimate was included in the census count.

Overall, the required adjustment to the Census figures "as collected" is estimated to be 2.71 percent for Australia as a whole, but varies not only from State to State but also between areas within States. Under-enumeration figures were determined by the Post-Enumeration Survey which was s sample survey conducted two weeks after the Census. All persons selected for inclusion in the survey were asked questions from the Census schedule by specially trained interviewers. The aim of the survey was to establish how effectively the Census operation contacted everyone in Australia on Census night and how well the questions were answered.

Estimated resident total population figures for local government areas (LGA's), States and Territories, which are available in separate publications, include an adjustment for under-enumeration. However, statistics available from the census are not adjusted for under-enumeration.

(b) Respondent error

The editing procedures previously described are not able to detect all errors made by individuals in completing the census schedule so that some errors may survive in final output. For example, if a respondent states his occupation as a doctor and he is really a clerk, the census coders will code him to the code for doctor. However, if his occupation is stated as a doctor but his age is recorded as 4 years, this combination is defined by census processing rules as unacceptable and will fail a consistency edit.


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