In the previous sections, we spoke extensively about how topic models, in general, are rather qualitative in nature - it's difficult to put a number on how useful a topic model is. Despite this, there is a need to evaluate topic models, and the most popular method out there is topic coherence - and lucky for us, Gensim has quite an extensive suite of topic coherence methods for us to try out.
What exactly is topic coherence? Briefly put, it is a measure of how interpretable topics are for human beings. There are multiple coherence measures in topic modeling literature, and we won't be going through the theory for these, but the following links should walk you through the theory and intuition, if interested:
The first link is a Gensim blog post...