Among the 200 highest-revenue books in each group, those with substantial detected AI text contained 4.4 percentage points more rare expressions from existing books. The study found that, among top-selling self-published genre books on Amazon, books with substantial detected AI text contained more rare expressions from existing books than books with no detected AI text. Among the 100 highest-revenue books with substantial detected AI text and the 100 highest-revenue books with no detected AI text, rare expressions from existing books covered 43.2% and 37.6% of the text, respectively. The team also compared the two sets of top-selling self-published genre books – those with substantial detected AI text and those with no detected AI text – with a separate reference set of award-winning or nominated literature. Rare expressions from existing books covered an average of 19.1% of the text in the literary reference set, compared with 37.2% in the top-selling books with no detected AI text and 41.6% in those with substantial detected AI text.