DATA CONSISTENCY

CONSISTENCY BETWEEN WAVES

The ACLD is a longitudinal dataset using data from successive Censuses.

While the 2006, 2011 and 2016 Censuses had predominantly the same questions and were processed in a similar way, there were some differences between them.

Users are encouraged to read Understanding the data pages in Census of Population and Housing: Understanding the Census and Census Data, Australia, 2016 (cat. no. 2900.0), and information in How Australia Takes a Census, 2011 (cat. no. 2903.0) and 2006 Census reference & information for information to assist with using and interpreting specific data items across time.

For example, a number of changes were made to how industry of employment information was collected for the 2016 Census. The ABS advises this data is not directly comparable to the previous Census Industry of employment data, and should not be used to measure longitudinal transitions between industries from 2011 to 2016. For further information refer to Industry of Employment (INDP) in Census of Population and Housing: Understanding the Census and Census Data, Australia, 2016 (cat. no. 2900.0).

There were widespread changes in the geography standard between 2006 and 2011 leading to the formation of the Australian Statistical Geographic Standard. In order to facilitate comparison, a 'best fit' of 2006 collection districts to align with the current geographic boundaries was created, however in some cases this will be an approximation only.

Other data items that are different between Census years are personal, family and household income. Income was collected in ranges and these ranges are different in different Census years. The ACLD does not include an adjustment to income data for inflation.

A small percentage of linked records have inconsistent data, such as a different country of birth at the different time points or an age inconsistency of more than one year. Inconsistencies may be due to:

• false link - the record pair does not belong to the same individual
• reporting error - information for the same individual was reported differently in 2006, 2011 and in 2016
• processing error - the value of a data item was inaccurately assigned or imputed during processing.

CONSISTENCY WITH OTHER SOURCES

Estimates derived from the ACLD may differ to those derived from other sources. This is due to a range of factors including:

Collection methodology

The ACLD is derived from Census data that is self reported by households across Australia on Census night. This will differ from other ABS collections which may rely on different collection methodologies (e.g. trained interviewers, administrative sources). In addition, the way survey questions are phrased and the answer options available for a given question may affect the information provided by respondents.

Reference period

The reference periods for the ACLD are the Census nights of each year. Other collections may use different reference periods.

Sampling methodology

The ACLD uses a 5% sample of Census data as its base population. This will differ from other collections that may collect information from the entire population of Australia (e.g. the Census) or from a sample of dwellings (e.g. Labour Force Survey).

Sampling and non-sampling error

While every effort is made to minimise error, each collection will have some level of error. Survey collections are subject to some level of sampling error, as they are based on information obtained from a sample of dwellings or businesses. The Census is not subject to this type of error, but is subject to some level of undercount. The ACLD is constructed using a sample of records from the Census, and is therefore subject to a level of sampling error of its own.

Scope and coverage

The ACLD weights benchmark the linked records to the longitudinal population that was in scope of consecutive Censuses. This will be different to cross-sectional estimates which may be benchmarked to a point-in-time population, such as the Estimated Resident Population.

Linkage error

The ACLD is subject to linkage error, as records from one Census are linked to corresponding records from the subsequent Census. While every effort is made to minimise false links, they can occur. Linkage error will not be apparent in other collections which are not produced through data integration.

For these reasons, while the results from the ACLD are considered to be broadly representative of the Australian population, they are not strictly comparable with statistics derived from other collections.

For detailed information about the different methodologies for each collection, refer to the Explanatory Notes within each release.

For detailed information regarding the differences between the Census and Labour Force collections, refer to The 2016 Census and the Labour Force Survey in Census of Population and Housing: Understanding the Census and Census Data, Australia, 2016 (cat. no. 2900.0).

For further information about the ACLD linkage methodology refer to Information Paper: Australian Census Longitudinal Dataset, Methodology and Quality Assessment, 2011-2016 (cat. no. 2080.5).