On a discussion thread on Facebook, this led to a proposal from me for measuring the general quality of a quote. Assume a user has some level of discrimination $$D$$; the higher the value of $$D$$, the more likely they are to quote a passage. Now assume each passage has some measure of quality $$Q$$; the higher the value of $$Q$$, the more likely a passage is to be quoted. Let's try a classic Bradley-Terry-Luce model - if a user with discrimination $$D$$ quotes at least one passage from a particular work, the probability $$p$$ that they'll quote a given passage with quality $$Q$$ from that same work is roughly $p = \frac{Q}{Q+D}.$