Report on the quality of 2021 Census data: Statistical Independent Assurance Panel to the Australian Statistician

The 2021 Census was conducted at a unique time in Australia’s history, with enumeration occurring during the COVID-19 pandemic when much of south-eastern Australia was in lockdown on or about Census night. All censuses aim to provide a timely, contemporary, and detailed view of the circumstances of Australia’s people and communities, but the 2021 Census is particularly important as it provides a view of Australians and Australia during the pandemic.

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

The Panel has concluded that the 2021 Census data is fit-for-purpose, is of comparable quality to the 2011 and 2016 Censuses and can be used with confidence.

The high response rate for private dwellings (96.1%) was an outstanding achievement given the challenges provided by the pandemic and is comparable to response rates seen in other countries, such as Canada and the United Kingdom, which undertook censuses during the pandemic, and higher than that of New Zealand, where the census was conducted pre-pandemic.

The 2021 Census paints a comprehensive and detailed picture of Australia’s population. This was enhanced by the inclusion of two new topics, namely Long-term health conditions and Australian Defence Force service, which were the first significant changes to the information collected on the Census since 2006.

In forming its view, the Panel examined a number of key topics, including Sex, Age, Income, counts of Aboriginal and Torres Strait Islander peoples, Country of birth, Language, Ancestry and Religion. The Panel’s analysis revealed that the items reviewed have results which are consistent with previous censuses and/or independent data sources and/or align with observations consistent with expected societal change or pandemic impacts, especially when interpreted in association with the Australian Bureau of Statistics (ABS) quality assessments.

The 2021 Census population counts align well with expectations. Counts of the population at the national and state and/or territory level derived from the 2021 Census, adjusted by the Post Enumeration Survey, compare well to the Estimated Resident Population, Australia’s official population estimate, and can be used to rebase these estimates.[1] Key quality indicators from the Post Enumeration Survey support the comparability of the 2021 and 2016 Censuses, with some improvements observed. The net undercount rate for persons on Census forms decreased from 3.7% to 2.8% between 2016 and 2021, and their gross overcount has remained stable at 1.2%.

The Panel considers that the Census is clearly fit-for-purpose for all of its uses, including the most important uses like rebasing the population estimates.

Alongside these findings, the Panel has made several observations.

[1] The Panel is not in a position to make a judgment about data quality below the state and/or territory level due to time constraints.

The 2021 Census was conducted at a time when many parts of Australia were in lockdown and movements within, into and out of Australia were tightly controlled. The ABS faced difficulties with recruitment of field officers, reflecting a tight labour market, and other challenges caused by the pandemic, such as restrictions on the movement of field staff both intra and interstate. Nevertheless, through appropriate planning, risk management, and rigorous testing, disruptions to Census field operations due to the pandemic were largely overcome without impact on the quality of Census data or safety of the public and Census staff. The Panel considers that the ABS’s approach to conducting the 2021 Census during the pandemic was impressive and well managed.

The Panel observed the expected impact of COVID-19 on peoples’ movements within, into and out of Australia across a range of census data items, including the expected declines in foreign student populations and the impact of almost no permanent migration for an extended period. In addition, more people were counted at home in the 2021 Census than previously, due to reduced population movement prior to and during the time of the Census. This has enhanced data quality.

The ABS introduced a number of important innovations in the 2021 Census and these served Australians well by improving the Census experience. The introduction of new online self-service options greatly assisted data collection, as did the total redevelopment of the online Census form. The form’s ease of use proved especially useful given the disruptions to field operations because of COVID-19 restrictions – people could easily access help and the online form, which they did, and in much larger numbers than in previous censuses.

In reviewing the 2021 Census data, the Panel identified some opportunities to enhance future censuses. The Australian Bureau of Statistics should consider:

1. Reviewing the results from the Census and Post Enumeration Survey for insights into any systemic gaps in the Address Register.
2. New opportunities for improving response rates in remote and regional areas, including innovations in enumeration methods.
3. Innovative solutions, including the use of administrative data, to improve the undercount of Aboriginal and Torres Strait Islander peoples, in partnership with Aboriginal and Torres Strait Islander peoples.
4. Opportunities to refine and enhance further the processes of occupancy determination and imputation for non-responding households, using administrative data.
5. Analyse the level of improvement to census data from the use of electricity data, with a view to the potential use of dwelling level data in the 2026 Census.
6. Continue to develop innovative options to enhance user experience and encourage response for the 2026 Census.
7. As part of the consideration of content for the 2026 Census, evaluate the two new topics, Australian Defence Force service and Long-term health conditions, to inform the value of their continued inclusion in the 2026 Census.
8. The Statistical Independent Assurance Panel should be continued for future Censuses to provide greater transparency, accountability and assurance.

This report has been authored by the 2021 Census Statistical Independent Assurance Panel. Members of the Panel are:

• Panel Chair Professor Sandra Harding, AO
• Ms Leanne Liddle
• Professor Peter McDonald, AM
• Mr Peter Morrison
• Mr Dennis Trewin, AO
• Mr Stephen Walters

The Statistical Independent Assurance Panel acknowledges the Traditional Owners and Custodians of Country across Australia and their continuing connection to land, waters and Community. We pay our respects to their cultures and their Elders past and present.

Recommended citation: Harding, S. Liddle, L., McDonald, P., Morrison, P., Trewin, D., Walters, S. (2022). Report on the quality of 2021 Census data. Retrieved from https://www.abs.gov.au/census/about-census/census-statistical-independent-assurance-panel-report

Professor Sandra Harding, the Panel Chair, provided the Panel's report to Dr David Gruen, the Australian Statistician. Professor Harding's transmission letter and Dr Gruen's acceptance letter can be found in Census Statistical Independent Assurance Panel findings.