machine learning – Why does lower perplexity indicate better …

The perplexity, used by convention in language modeling, is monotonically decreasing in the likelihood of the test data, and is algebraicly equivalent to the inverse of the geometric mean per-word likelihood. A lower perplexity score indicates better generalization performance. I.e, a lower perplexity indicates that the data are more likely.

https://stats.stackexchange.com/questions/273355/why-does-lower-perplexity-indicate-better-generalization-performance