title: Coherence score (u_mass) -18 is good or bad?
body: <p>I read this question (<a href="https://stackoverflow.com/questions/54762690/coherence-score-0-4-is-good-or-bad">Coherence score 0.4 is good or bad?</a>)  and found that the coherence score (u_mass) is from -14 to 14. But when I did my experiments, I got a score of -18 for u_mass and 0.67 for c_v. I wonder how is my u_mass score out of range (-14, 14)?</p>
  
  <p>Update: I used gensim library and scanned   the numbers of topics from 2 to 50. For u_mass, it starts from 0 to the lowest negative point and turn back a bit, like an upsidedown version of c_v.</p>