CONTACT SECTOR

Net undercount in the contact sector for a given category of person can be disaggregated into four sub-components:

• Gross undercount
• Gross overcount
• Net difference in classification
• Persons with a Census not stated category.

The following table illustrates this disaggregation for broad Country of birth categories. Descriptions of the four sub-components are provided below.

	PES population estimate		Census count		Gross undercount		Gross overcount		Net difference in classification		Persons with Census category not stated		Net undercount in contact sector (a)(b)
	no.		no.		no.		no.		no.		no.		no.
Born in Australia	16 124 161		15 189 883		767 068		172 412		47 422		292 201		934 278
Born overseas	6 369 428		6 017 963		383 521		102 261		-47 422		117 627		351 465
Not stated	–		409 828		–		–		–		–		–
Total Persons	22 493 589		21 617 674		1 150 588		274 673		–		–		875 915

– Nil or rounded to zero (including null cells).
(a) Components of net undercount for Country of birth do not add to the total, as those with a not stated value do not contribute to the Census counts used to calculate net undercount for a given category.
(b) The net undercount is equal to the sum of the Gross undercount, the Net difference in classification and the Persons with a Census not stated category, minus the Gross overcount.


GROSS UNDERCOUNT

Gross undercount for a category is an estimate of the number of people who should have been counted in that category in the Census (according to PES) but were missed because:

• they were not included on a completed Census form at their usual residence or another dwelling
• their dwelling was not known to Census (e.g. it was not included on the ABS Address Register or was not located by a Census Field Officer)
• their dwelling was mistakenly deemed unoccupied on Census night.

The PES estimated that 1,150,588 persons were missed in the Census in 2016.

As Census was unaware of these persons and dwellings and therefore no imputation was performed, this component is separate from the persons imputed into non-responding dwellings, which forms part of the non-contact sector.

GROSS OVERCOUNT

Gross overcount for a category is an estimate of the excess count of persons in that category (according to PES) either from being counted on more than one Census form or from being counted in error (e.g. where a person was overseas on Census night and should not have been counted, but was included on a Census form at their usual residence). In 2016, 274,673 persons were estimated as having been overcounted in the 2016 Census, compared with 144,341 persons in 2011.

NET DIFFERENCE IN CLASSIFICATION

Occasionally, responses obtained for a person in the PES interview are not consistent with those obtained for the same questions in the Census. In addition, a value that was imputed in the Census for a missing response (e.g. Age, Sex, or State/Territory of usual residence) is likely to 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. In 2016, for example, a net difference of 47,422 persons contributed to the net undercount estimates for Australia-born (according to their response in PES), even though they were counted as born overseas in the Census. For more information, see Technical Note 1: Differences in Classification between the PES and Census on the Explanatory Notes tab.

PERSONS 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, Registered marital status, and State/Territory of usual residence 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).

To create benchmarks for Indigenous status and Country of birth for PES estimation, persons in the contact sector with a Census category value of not stated for these items had their Census response imputed during PES processing. For details on this process, see ‘Resolution of Census Not Stated Values for PES’ in Census Counts on the Explanatory Notes tab. In 2016, there were 409,828 persons who had a missing value for Country of birth in the Census contact sector. An estimated 292,201 of these were imputed as born in Australia and therefore contributed to the net undercount for that category.

CALCULATING NET UNDERCOUNT FOR THE CONTACT SECTOR

The net undercount for a category of person in the contact sector (e.g. those born in Australia) is equal to the sum of persons undercounted in the Census (i.e. gross undercount), persons with a net difference in classification between PES and Census, and those with a not stated response in the Census who should have been counted in the particular category, then subtracting those persons who were overcounted in the Census (i.e. gross overcount) in that category.