Basic Performance Measures for Information Retrieval
Precision and recall and their combinations are the most common measures for evaluating the performance of information retrieval systems. These measures require a collection of documents, a query, and a set of relevance judgments.[more]
Mark a retrieved item as relevant or irrelevant by clicking it and watch how measures change. Relevant items are denoted by a light purple background when clicked. Mouseover the measures to see their definitions.[less]
"Information Retrieval" on Wikipedia.