According to (Ehling et al., 2007), for each source sentence with N different translations, we could select the final translation based on the following Minimum Bayes Risk principal: e = arg min e { e (P r(e |f ) • (1 − BLEU (e , e)))} (6) Here P r(e |f ) denotes the posterior probability for translation e and BLEU (e , e) represents the sentence-level BLEU score for e using e as reference.
since the translation hypotheses are generated under different groups of weights, the corresponding posterior probability is no longer comparable.