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Census of Population and Housing: Census dictionary
Reference period

Improvised home

These include sheds, tents, humpies and other improvised dwellings, occupied on Census night. This category also includes people sleeping out, such as those sleeping on the streets, in abandoned buildings, under bridges or in cars.  

See also Homelessness enumeration and Dwelling structure (STRD).

Imputation variables

Imputation flag variables enable users of Census data to quantify the number of imputed records (for applicable data items: age, sex registered marital status etc.) in a given population.

See also Derivations and imputations.

Intelligent Character Recognition (ICR)

2021 Census data was processed using Intelligent Character Recognition (ICR) technology for the paper forms. Specialised computer software is used to interpret the handwriting on images taken of each page of the Census form. Once recognised, answers to Census questions were coded to the appropriate category of the relevant classification, for example Religion, Occupation, etc.

See also Data processing.

Internal migration

Internal migration is the movement of people across a specified boundary within Australia for the purpose of changing their place of usual residence. Information on internal migration within Australia is available from the Census.

The Census asks a series of questions relating to each person's usual address which can be used to identify the change of address of people for one year prior to the Census data, and for five years prior to the Census date. Data collected in the Census only reflect movements which coincide with these particular points in time in the intercensal period (i.e. one year ago and five years ago), even though there may have been multiple movements during this period.

Household mobility indicators are also derived using this information. Note that persons temporarily absent, visitors, and households containing only visitors, are excluded from these variables. 

See also Household one year mobility indicator (MV1D), Household five year mobility indicator (MV5D), Place of usual residence one year ago (PUR1P), Place of usual residence five years ago (PUR5P),  Usual address indicator Census night (UAICP), Usual address one year ago indicator (UAI1P), Usual address five years ago indicator (UAI5P), and Usual residence.

Interviewer Household Form

The Interviewer Household Form is used in Aboriginal and Torres Strait Islander communities (and areas where language differences or other factors make use of the standard self-enumeration forms impractical). The Interviewer Household Form is an interview based Census form which is used to record the details of up to 12 people in a household, and some dwelling data. If there are more than 12 people in a dwelling, additional Interviewer Household Forms are used.

Introduced random error/perturbation

Under the Census and Statistics Act 1905 it is an offence to release any information collected under the Act that is likely to enable identification of any particular individual or organisation. To minimise the risk of identifying individuals in aggregate statistics, a technique has been developed to randomly adjust values. Random adjustment of the data, known as random error or perturbation, is considered to be the most satisfactory technique for avoiding the release of identifiable data while maximising the range of information that can be released.

See also Confidentiality.

Item non-response

Item non-response occurs:

  • where a household or person returns a form but does not answer one or more questions (items) - these are 'item non-response'
  • where a household does not return a form and key variables for a non-responding person have been imputed, the remainder of questions (items) are either set to 'item non-response' or 'not applicable', dependent on the imputed age of the person.

Item non-response rates include households and persons who did not answer a question (item) as well as imputed (non-responding) households and persons.

See also Dwelling non-response and Person non-response.