Earlier quoted context omitted.
Yes, I missed that, even though it is very clearly spelled out (oops!). It makes the ordinal comparison valid (modulo noise), but it does not completely address the concern. If you have two artists, and artist 1 uses 5,000 unique words in 35,000 lyrics while artist 2 uses 10,000 unique words in 35,000 lyrics, artist 2's vocabulary may be substantially more than twice as large as artist 1's. It is unlikely that a lyri…
This is a very good point - Aesop Rock, for example, uses one unique word every 5 words (7k unique in 35k), and if this does not stop, maybe he would continue and we would find the same average in 70k or 120k words. After all, you still have to have filler words like "to", "a", "the", "have", etc - he could be saturating the spots where he can put uniques. So this could substantially underrepresent vocabularies. Ther…
A second related problem that that paper touches on toward the end is that sequential words from the same text are not independent samples from an author's vocabulary. Two artists may have the same vocabulary, but if one artist uses more non-sequiturs, fewer articles, fewer repeated phrases, or generally tries to use more unique words within a given song, then that artist will come out ahead in the measure used here. I'm not sure how much of a problem this really is for comparing lyrics between artists (depending on what is of interest, it may actually be desirable), but it may explain the poor showings for Shakespeare and Melville, since prose is likely to repeat words more frequently than rap lyrics for reasons unrelated to the authors' vocabularies. (FWIW, even conservative estimates put Shakespeare's vocabulary at >15,000 words, which would be hard to measure in a sample of 35,000 words.)