Undercounting and/or underenumeration
Census collectors direct extensive efforts toward locating dwellings and households within districts, however locating them all is sometimes not possible. Some dwellings may not be identified. For example, in commercial areas, flats above or behind shops may be difficult to find. Also, particularly where contact is not made at delivery, flats behind or attached to private dwellings may not be included in the Census. Analysis of the undercount in previous Censuses has shown that people away from their usual residence on Census Night (for example, travelling, camping, staying in a non-private dwelling, or visiting friends) are more likely to be missed than people at home on Census Night.
Even when a household is found, undercount is possible if not all members of the household are included on the form (for example, if there are more than six people in the household and no extra forms are obtained) or if the household, or a member of the household, refuses to cooperate and complete a Census form.
A measure of the extent of underenumeration is obtained from the Post Enumeration Survey (PES). The official population estimates produced by the ABS take into account the results of the PES. However, the Census counts are not adjusted.
See also Post Enumeration Survey (PES).