Success at n
Success at n is an information retrieval relevance measure, equal to 1 if the top-n documents contain a relevant document and 0 otherwise. When averaged across multiple queries, the success rate at n indicates how often something relevant was retrieved within the top-n.
A system with a high success rate will be one that rarely retrieves zero relevant documents. Therefore, success rate can be employed to monitor failure. The success rate of two systems may differ even if they have the same mean precision at n, because one system has higher variance than the other. Success at n models the satisfaction of a user who does not need to see many relevant documents, is prepared to view up to n results and is disappointed by a completely irrelevant top-n.