13. A computer program product for providing assistance in detecting mistranslation in a translated document obtained by performing machine translation of an original document, the computer program product comprising: a computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising: computer readable program code configured to obtain a word included in the translated document; computer readable program code configured to obtain a first value representing the search results of performing a web search of a first document data group and a second value representing the search results of performing a web search of a second document data group including the first document data group for pieces of document data related to the word obtained by the first acquisition unit, wherein the first document data group is obtained from a specific website known to be relevant in a subject matter field for the obtained word, and wherein the second document data group is obtained through a general web search; computer readable program code configured to generate, based on a comparison of the ratio of the first value and the second value with a predetermined threshold value, an index indicating adequacy of the obtained word as a translated word in a subject matter field corresponding to the first document data group; and computer readable program code configured to output the generated index.
16. The computer program product according to claim 13 , wherein: the computer readable program code configured to obtain a word includes computer readable program code configured to obtain a compound word that includes a plurality of constituent words, and the computer readable program code configured to obtain search results includes computer readable program code configured to obtain the search results of searching both the first document data group and the second document data group for pieces of document data that include the plurality of constituent words as the pieces of document data related to the word.