## What does perplexity mean in NLP?

## What is perplexity in machine learning?

**Perplexity**measures how well a probability**model**predicts the test data. The**model**that assigns a higher probability to the test data is the better**model**. [A good**model**will assign a high probability to a real sentence]

## What is perplexity and why does it matter?

**Perplexity**is a metric used to judge how good a**language model**is We can define**perplexity**as the inverse probability of the test set, normalised by the number of words:

## What is the perplexity of a test set?

- For a test set W = w1, w2, …, wN, the perplexity is the probability of the test set, normalized by the number of words: This equation can be modified to accommodate the language model that we use. For example, if we use a bigram language model, then the equation can be modified as follows;

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