What is document length normalization?

Document length normalization is a technique in information retrieval that adjusts the influence of document length on its relevance score. In document ranking systems, longer texts may have more matches with the query simply due to their size, which can distort the results.

Normalization of document length helps to reduce this effect by bringing the document's weight to a comparable scale regardless of its size. For example, the BM25 model uses a parameter that considers the document length relative to the average length in the collection to balance the contribution of long and short documents.

Thus, document length normalization helps to make ranking more fair and accurate, improving search quality.