Erratum To 'A Statistical Approach To Machine Translation'

In Section 6 of "A statistical approach to machine translation" (Computational Linguistics 16(2), 79-85), we reported the results of two experiments in which we estimated parameters of a statistical model of translation from English to French. In the first experiment, the English and French vocabularies each consisted of 9,000 common words, and the model parameters were estimated from 40,000 pairs of sentences 25 words or less in length. Words outside the 9,000-word vocabularies in these sentences were mapped to special unknown words. In the second experiment, the vocabularies were limited to 1,000 common English words and 1,700 common French words, and the model parameters were estimated from 117,000 pairs of sentences 10 words or less in length that were completely covered by the respective vocabularies. In Figures 4, 5, and 6 of the paper, we erroneously presented parameter estimates from the 1,000-word experiment, while claiming in the text that they were from the 9,000-word experiment. The parameter estimates for these two experiments differ considerably because of the restriction of the training corpus in the 1,000-word experiment to short, covered sentences. For example, the probability that hear is translated as bravo