It looks like they didn't include podcasts. Given the rise of various podcasts that are basically serialized audiobooks, I have to wonder what the numbers would be like including them.

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renjimen a day ago | parent [-]

One of their primary motivations was understanding changes in literacy, so it makes sense they wouldn't include audiobooks (or podcasts).

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ascorbic a day ago | parent [-]

They do include audiobooks

	▲	renjimen a day ago \| parent [-]
		Ah, I misunderstood the parent then :) Seems unintuitive to include audiobooks if they're interested in literacy though (literally their first motivation).