Here's a flawed starter method: take all books made into films.
Get \(a =\) average of these books' scores, \(b =\) average of those films' scores, \(c =\) average of the young-adult subset books' scores, and \(d =\) the average of the young-adult subset films' scores.
\(b/a\) is the general book-to-film conversion loss.
\(d/c - b/a\) is the specific young adult conversion loss.
(This doesn't decompose the book-status and commercial-pressure effects, you'd need natural experiments for that.)