Yeah because it’s primary research and this is a huge unaddressed and uncared about problem that’s only growing. The last National Assessment for Adult Literacy took place in 2003.
PIAAC (PROGRAM FOR THE INTERNATIONAL ASSESSMENT OF ADULT COMPETENCIES) which this is likely partially based on is typically who provides the survey data to these institutions.
Barbara Bush Foundation is another source that deals specifically with this.
A lot of this data is cobbled together because the government has practically defunded any studies of this issue. Literacy has effectively been taken for granted and hasn’t actually been upheld. Everyone in this space says more data is needed but isn’t optimistic that more data is going to paint a better picture of literacy (both in children and adults) in the US.
Audiobooks aren’t really a good solution to be honest. Reading / writing literacy are the basis of scholarship. We have centuries of research and examples that we’ve turned our back on that efficient learning happens only when you can unlock good literacy skills. Specifically the aspect of reading/physical writing/sublingualization is a cornerstone of comprehension of complex ideas. With something like Marxism that’s based on understanding both technical and archaic language and social constructs it becomes really hard. There are tons of self professed Marxists that couldn’t tell you what commodity fetishism actually means in simple terms.
Great example is the Communist Manifesto itself, meant to be a pamphlet for factory workers in the 19th century, but is typically a mildly difficult text to approach for the average person today.
Audiobooks can replace something like pleasure reading where you’re just reading pulp garbage, but they’re not really a good replacement for learning.