title: Can we use NDCG as a recommender system metric when the relevance to the recommended item is in binary form?
body: <p>Generally there is a relevance associated with item in ndcg calculation but if we only have feedback in 0/1 form. Eg</p>
  
  <p>list ={1,0,0,0,1} when we have recommended 5 items (first and last items are relevant here)
  How do we calculate ndcg here ? and does order matters in ndcg evaluation  ?</p>
  
  <p>Also what metrics are useful for evaluation in a binary feedback based recommendation ?</p>