Finally, for each target phrase t in the phrase table we compute the ratio of the perplexity of t according to the original language model L o and the perplexity of t with respect to the translated model L t (see Section 4).
the factor F is computed as follows: We apply these techniques to the French-to-English and English-to-French phrase tables built from the mixed corpora and use each phrase table to train an SMT system.