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Perplexity

Language Model Perplexity

Definition

Perplexity is a metric for evaluating language models that measures how well the model predicts a held-out text sample. It is the exponentiated average negative log-likelihood per token — lower perplexity indicates the model assigns higher probability to the test text.

Perplexity is a standard intrinsic evaluation metric but correlates imperfectly with downstream task performance.


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