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COMPONENTS OF NET UNDERCOUNT
This section provides additional information on these components to assist in the interpretation of estimates of net undercount presented in this publication.
Contact and non-contact sector
Table 13 provides estimates of the key components of net undercount, the definitions of which follow the table. For the purposes of PES estimation, Census dwellings deemed occupied on Census night are divided into a 'contact' sector (dwellings for which a Census form was received before the commencement of PES enumeration) and a 'non-contact' sector (where no Census form was received or a Census form was received after the commencement of PES enumeration - that is, a 'late return').
Persons missed in the Census in the contact sector
For a given category of person as reported in the PES (e.g. 'Males' recorded in the PES), 'Persons not counted in the contact sector' is the difference between the number of people in that category that should have been counted in the Census and the number of people in that (PES) category that were counted on Census forms (irrespective of their Census category).
Net difference in classification in the contact sector
Occasionally, the responses obtained for a person in the PES interview are not consistent with those obtained for the same questions in the Census. In addition, where a value has been imputed in the Census for a missing response (for example, Age, Sex, or State/territory of usual residence), it may differ from the PES response.
The net difference in classification for persons actually counted in the Census contact sector is equal to the estimated number of people in the given category as reported in PES, minus the number counted in that same category in the Census. For more information see the Differences in classification Technical Note (in Explanatory Notes).
Persons (in the contact sector) with Census category not-stated
The Census contact sector contains some dwellings which were responding in the Census but returned only a partially completed Census form. For Census purposes, values for Age, Sex, State/territory of usual residence and Marital status are imputed during Census processing in cases where these items have been left blank. Missing values for other items remain 'not-stated' in the final version of Census counts (including Indigenous status and Country of birth). Persons in the contact sector with a Census category value of 'not-stated' contribute to net undercount estimates for the category in which they should have been counted as reported in the PES (e.g. Indigenous status).
Undercount in the non-contact sector
Non-responding dwellings in the Census are dwellings where the Census never obtained a return, and the dwelling could not be established as having been unoccupied on Census night. During Census processing, a 'hot-deck' imputation method (see Glossary) was utilised to impute people and their Age, Sex, Marital status and Place of usual residence into these dwellings. These values were, in many cases, based on information provided by the Census collector about the dwelling and its residents. Values for all other variables (e.g. Indigenous status) were set to 'not-stated' or 'not applicable', depending on the imputed value for Age.
Inevitably, the imputed values differ from the true but unknown values.
Imputed records made up the majority of the 2011 Census non-contact sector. Late returns made up only a small proportion of this sector.
An estimate of the undercount in the non-contact sector for a category of person is obtained by calculating the difference between the PES estimate of the number of people who should have been counted in the non-contact sector in that category (as reported in the PES) and the Census count of people in the non-contact sector for the category (including imputed person records within the category). For a category of persons classified by Age, Sex, Marital status and State/territory of usual residence, this component of net undercount largely represents an estimate of imputation error in the Census for this category of imputed persons. For the Indigenous status and Country of birth categories, this component largely represents an estimate of persons who should have been counted in this category in non-responding dwellings.
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