Average Precision

Definition

Average precision is a measure that combines recall and precision for ranked retrieval results. For one information need, the average precision is the mean of the precision scores after each relevant document is retrieved.

$$Average\,Precision = {{\sum\nolimits _{r}P @ r}\over {R}}$$

where r is the rank of each relevant document, R is the total number of relevant documents, and P@r is the precision of the top-r retrieved documents.

Key Points

The average precision is very sensitive to the ranking of retrieval results. The relevant documents that are ranked higher contribute more to the average than the relevant documents that are ranked lower. Changes to the ranking of relevant documents have a significant impact on the average precision score. Average precision is considered a reasonable evaluation measure for emphasizing returning more relevant documents earlier.

Cross-references

MAP

Mean Average Precision

Precision

Precision at n

P@n

Recall

Standard Effectiveness Measures