Detecting semantically equivalent questions is a very difficult task due to two main factors: (1) the same question can be rephrased in many different ways; and (2) two questions could be asking different things but look for the same solution.
traditional similarity measures based on word overlap such as shingling and Jaccard coefficient (Broder, 1997) and its variations (Wu et al., 2011) are not able to capture many cases of semantic equivalence.