I didn’t look into the details of the survey described in this article. A large international survey that covers literacy is PIAAC[1]. You can read about their

I didn’t look into the details of the survey described in this article. A large international survey that covers literacy is PIAAC[1]. You can read about their ‘levels’ of literacy in one of their reader’s guides[2]. The survey suggested that 17.6% of adults in the US score at level 1 or below (basic vocabulary, ability to extract a single piece of information in a short text) and 12.8% of US adults score at level 4 or 5. People with low literacy tend to struggle with vocabulary, or large blocks of text, and will be slow readers who can’t skim text. You can find some practical descriptions of low literacy in UX articles like https://uxpamagazine.org/people_who_do_not_read_easily/ https://uxpamagazine.org/people_who_do_not_read_easily/ or https://gds.blog.gov.uk/2016/02/23/writing-content-for-everyone/ https://gds.blog.gov.uk/2016/02/23/writing-content-for-every... [1] https://www.oecd.org/en/about/programmes/survey-of-adult-skills-piaac.html https://www.oecd.org/en/about/programmes/survey-of-adult-ski... [2] See pages 115-116 of https://www.oecd-ilibrary.org/education/the-survey-of-adult-skills_cf22f417-en https://www.oecd-ilibrary.org/education/the-survey-of-adult-...