VOCABULARY SIZE ESTIMATION APPARATUS, VOCABULARY SIZE ESTIMATION METHOD, AND PROGRAM

A vocabulary size estimation apparatus includes a question generation unit configured to select a plurality of test words from a plurality of words, a presentation unit configured to present the test words to users, an answer reception unit configured to receive answers regarding knowledge of the test words of the users, and a vocabulary size estimation unit configured to obtain a model representing a relationship between values based on probabilities that the users answer that the users know the words and values based on vocabulary sizes of the users when the users answer that the users know the words, by using the test words, estimated vocabulary sizes of people who know the test words, and the answers regarding the knowledge of the test words. The question generation unit selects, among the plurality of words, words whose degrees of adequacy of notations meet a predetermined criterion as the test words.