Dense retrieval models (e.g. DPR) achieve SOTA on various datasets. Does this really mean dense models are better than sparse models (e.g. BM25)?
No! Our #EMNLP2021 paper shows dense retrievers even fail to answer simple entity-centric questions.

arxiv.org/abs/2109.08535 (1/6) We construct EntityQuestions, consisting of simple, entity-rich questions such as “Where was Arve Furset born?”. We find dense retrieval models drastically underperform sparse models! (2/6)