NDCG
#evaluation #ranking #retrieval #recommendation
NDCG (Normalized Discounted Cumulative Gain) measures the quality of a ranking system, considering the position of relevant items in the ranked list while giving more weight to the items placed higher. So it considers both the relevance and the position of items in the ranked list.
It relies on the idea of cumulative gain, which measures the total item relevance in a list. To give more credit to the items higher in the ranking, it uses DCG (Discounted Cumulative Gain). DCG introduces a logarithmic discount to give lower weight to items further in the list.