A number of techniques have been investigated, including cosine similarity of feature vectors (Attali and Burstein, 2006) , often combined with dimensionality reduction techniques such as Latent Semantic Analysis (LSA) (Landauer et al., 2003) , and generative machine learning models (Rudner and Liang, 2002) as well as discriminative ones <cite>(Yannakoudakis et al., 2011)</cite> .