We measure the utility of our proposed LM adaptation approach in two ways: (a) comparing reference translations based perplexity of adapted LMs with the generic LM, and (b) comparing SMT performance of adapted LMs with the generic LM.
then, we select the top-N sentences which are similar to the development set, estimate the bias 4-gram LMs (with n-gram cutoffs tuned as above) with these selected sentences, and interpolate with the generic 4-gram LM as the adapted LMs.