1. Introduction

The Australian Bureau of Statistics (ABS) conducts a Census of Population and Housing (the Census) every five years. The data collected provides valuable information for policy making and research and is used widely, including setting electoral boundaries and other such applications.

On 18 June 2020, the ABS announced that Census night for Australia’s 18th Census would be 10 August 2021. The ABS planned the 2021 Census to achieve three strategic outcomes:

• Smooth running: The Census process is easy, simple, and secure.
• Strong support: Governments, businesses and the community have confidence in the Census and there is a high level of community participation.
• High quality data: Census data is high quality and widely used to inform on policy and areas of importance to Australia.

As in 2016, the 2021 Census was planned to be multi-modal, with the expectation that approximately 75% of Australian households would complete their Census online. This expectation was exceeded, with nearly 80% of responding households completing their Census online. This was enabled by the development of an entirely new online Census form and digital service, as well as the implementation of a communication campaign that supported a window of time to complete the Census, rather than a single night. The overall dwelling response rate for Australia was 96.1%, an excellent outcome given the target of greater than 95% and the challenges of the pandemic.

People were actively encouraged to complete their Census form online. A letter was delivered to most households with a unique login ID and instructions to complete online. Paper forms were delivered to households where completing online was less likely to be preferred or possible, and paper forms were also available on request to everyone in Australia. The ABS ensured a range of innovative approaches were used so that the enumeration of the entire population was as complete as possible. For the first time, people could complete their Census online without having a Census login code (see Appendix E).

The 2021 Census collected responses on two new topics: Long-term health conditions and Australian Defence Force service. These were the first significant changes to the information collected in the Census since 2006. Changes were also made to the way certain topics were collected. Notably, response categories of 'Aboriginal' and 'Torres Strait Islander' were added to the Ancestry question; respondents had the option of identifying as non-binary sex; and the Language question was updated to refer to language used (rather than language spoken), to enable inclusion of sign languages such as Auslan.

The emergence of the world-wide COVID-19 pandemic in early 2020 introduced a range of challenges across the globe for people, communities, governments, businesses, and countries. Australia experienced the pandemic through several waves during 2020, 2021 and 2022, resulting in the 2021 Census being conducted at a unique and challenging time in Australia’s history. Much of south-eastern Australia was in lockdown on or about Census night, equating to over half of Australia’s population. The ABS’s response was impressive and well managed. Further details on ABS’s management of the Census in the pandemic are available in Section 4 of this report ‘COVID-19 and the 2021 Census’.

The 2021 Census data, collected at such an important and unique time in Australia’s history, provides a timely, contemporary, and detailed view of the circumstances of Australia’s people and communities during the COVID-19 pandemic.

In recognition of the importance of Census data, and the importance of being transparent about data quality, the Australian Statistician established the 2021 Census Statistical Independent Assurance Panel (the Panel). The Panel was established in late 2020 to provide assurance and transparency for the 2021 Census data.

Such a panel had first been established following the 2016 Census. The Report on the Quality of 2016 Census data produced by the 2016 Census Independent Assurance Panel noted that the establishment of an Independent Assurance Panel should be repeated for future censuses. The ABS accepted this suggestion and all other opportunities identified by the 2016 Census Independent Assurance Panel. More information on how the opportunities identified in the 2016 report were addressed is provided in Appendix A.

This report presents the findings of the Panel following its review of the quality of the 2021 Census data and provides information to enable governments, the community, and other stakeholders to make an informed judgment about the fitness-for-purpose and credibility of the 2021 Census data.

The Panel, comprising a group of experts with diverse experience and backgrounds, was tasked by the Australian Statistician to provide an independent assessment of the quality and fitness- for-purpose of the 2021 Census of Population and Housing data.

The Terms of Reference for, and membership of, the Panel are in Appendix D.

The Panel undertook this review as a body independent of the Australian Statistician.

This report provides a high-level analysis of the quality of the 2021 Census data and focuses on key aspects of the Census data. It does not provide detailed quality reports on all data items or geographies.

The Panel was provided access to data from the 2021, 2016 and 2011 Censuses, data from the 2021 Post Enumeration Survey, information on Census processes, and other information as requested. The Panel was also provided Secretariat support from the ABS and engaged throughout the review process with ABS and Census officials.

Under its Terms of Reference, the Panel was required to consider the quality effects of Census design, enumeration, and processing, and to compare the 2021 Census results with the previous two Censuses and various other ABS and non-ABS data sets. The Panel also compared the quality indicators of the Census outputs against selected international censuses. The Panel’s assessment of quality was also guided by the accuracy framework described in Appendix C.