Discounted cumulative gain

Discounted Cumulative Gain (DCG) is a measure for ranking quality and measures the usefulness (gain) of an item based on its relevance and position in the provided list. For comparing different lists of recommendations with various lengths, normalized Discounted Cumulative Gain (nDCG/NDCG) is used. It is computed by dividing the DCG by the Ideal Discounted Cumulative Gain or IDCG. The higher the nDCG, the better ranked list.

Literature

• Markus Weimer, Alexandros Karatzoglou, Quoc Viet Le, Alex Smola: CofiRank - Maximum Margin Matrix Factorization for Collaborative Ranking, NIPS 2007

External links

• Wikipedia: Discounted cumulative gain
• C# implementation of DCG, IDCG, and nDCG for binary responses (part of the MyMediaLite library)
• CofiRank contains an implementation of an algorithm that optimizes NDCG (for ratings).