Reciprocal rank fusion

Also written: RRF

A simple way to merge two ranked lists: each document scores 1 ÷ (60 + its rank) in each list, and the scores are added.

The simplest merge that works well is called reciprocal rank fusion, or RRF. ("Fusion" means merging.) Every list a document appears in gives it some points: 1 ÷ (60 + its rank in that list). Then you add up each document's points and sort by the total.

Other terms from the same lesson

• BM25: The standard keyword-search score: it rewards documents that use the question's words, especially rare words, without over-rewarding repeats.
• hit rate: The share of test questions where the right document appears in the top k results.
• hybrid search: Combining keyword search with embedding search, so you get both exact-word matches and matches in meaning.
• keyword search: Finding documents that contain the words in the question. It catches exact names and codes that meaning-based search can miss.
• mean reciprocal rank: A search score: for each test question, 1 ÷ the rank of the first right document, averaged. 1 means the right one always comes first.
• reranker: A slower, more careful model that re-orders the top search results by how well each one actually answers the question.
• stopwords: Very common words such as "the" and "a" that keyword search ignores because they say little about what a document is about.