Various international organizations have performed a series of adult literacy surveys over the years.
1992 — NALS (National Adult Literacy Survey)
1994, 1996, 1998 IALS (International Adult Literacy Survey)
2003–2008 — ALLS (Adult Literacy and Life Skills Survey)
2011 PIAAC (Program for the International Assessment of Adult Competencies).
Extra focus on digital and mixed formats.
Data from these studies can be linked. On a scale from 1 to 5, they reveal the % of population that falls within each level. Looking at the results, it becomes clear that many of your target readers have more challenges that you might assume.
