Task: Question Answering
Input (English): For evaluation, the Visual Dialog task employs four metrics. NDCG is the primary metric of the Visual Dialog Challenge which considers multiple similar answers as correct ones. The other three are MRR, recall@k, and mean rank where they only consider the rank of a single answer. 
 Question: What metrics are used in challenge?
Output (English): NDCG MRR recall@k mean rank