In reply to @_catinthehat

You can read the full peer-reviewed study from UCL which examined sample bias in England’s 2018 PISA data here: https://johnjerrim.com/wp-content/uploads/2021/04/jerrim_2021_pisa_2018.pdf And you can find a (non-paywalled) high level summary of the key findings here: https://www.ucl.ac.uk/news/2021/apr/governments-education-statistics-seriously-flawed