This report covers the work of the Methodological Assurance Review Panel (MARP) from October
2020 to September 2021. In that period the Panel met 11 times and considered 28 papers detailing
methodologies across the entire Census programme. For a full list of papers assured during this
period, and the minutes of meetings where these were discussed, please visit the MARP minutes page. These documents should be regarded as annexes to this report.

Part of the Panel’s remit is to provide external, independent assurance and guidance on the
statistical methodology underpinning the 2021 Census. The Panel has examined every draft paper in
detail, both in preparation for the meeting, and in discussion at the meeting itself. The Panel is
satisfied that ONS has taken due account of its guidance and challenge, and that the final versions of
papers reflect this. This is in addition to ONS’s own peer review process of detailed methodology
where that is appropriate.

The pandemic has necessitated key changes to the Panel’s ways of working. Since March 2020, all
meetings have been held remotely, with shorter but more frequent meetings. The year’s main focus
has been the Census itself, which launched in March 2021. This work specifically on methodology
for the 2021 Census has continued past Census Day itself, with some topics being discussed after the
census date but prior to the live statistical processing and subsequent output production.

In addition, at the request of the National Statistician, the Panel has taken a more informal broader
role, of being kept abreast through regular informal briefings of key developments during Census
collection and processing. This has helped to identify potential risks to previously agreed processes
as well as providing an expert outside perspective where possible. It has also given additional
context for the Panel’s substantive discussions.

There has also been an increase in the number of papers on the future of population statistics
beyond the current Census. Over the next year, these workstreams are likely to dominate the work
of the Panel as outstanding 2021 methodological questions are finalised. These projects will
ultimately feed into the 2023 National Statistician recommendation on the future of the Census,
which will be a major focus for the work of the Panel in the next two years.

The year 2021 also saw the work of the Panel being more visible than previously. In particular the
Panel received open letters outlining support for alternative options for the 2021 Census sex
question guidance. There was close attention to a methodology paper on this question, but
ultimately the issue was resolved following Judicial Review.

The original members of the Panel, Oliver Duke-Williams, Nik Lomax, David Martin, Natalie Shlomo
and Bernard Silverman (chair), have continued to serve. They were joined in June 2021 by Ana
Basiri, Professor of Geospatial Data Science at the University of Glasgow. Professor Basiri will work
alongside existing members to assure methodologies for the Census, as well as social survey
transformation and the 2023 recommendation on the future of the Census.

Sir Bernard Silverman, Chair of the Methodological Assurance Review Panel