Clustering English Textbooks for Vocational Education Based on Lexical Similarity

As occupation fields become more fine-grained and specialized in the globalized world, the importance of English for vocational education becomes greater than the past. Currently, under the government authorization, several English textbooks for vocational high schools have been developed for 5 main vocational areas, i.e. agriculture, industry, commerce, marine and fishery, and domestic industry. However, little is known about with what criteria the textbooks were classified and grouped for each specified field under the five areas. The goal of this paper is to provide a principled and scientific method to classify the English textbooks for the five vocational areas. For this purpose, we collected English textbooks from 13 vocational fields and made a textbook corpus with the textbooks. For quantitative and statistical analysis, we adopted previous studies on linguistic similarity and a hierarchical clustering method. Our study proceeded as follows. First, we made a word list for each English textbook. Then, we calculated the percentage of lexical similarity along the word lists of 13 textbooks. Finally, we applied the hierarchical clustering method to producing a dendrogram of English textbooks for vocational education. Along the resulting dendrogram, we could identify which textbook was closer to which one, and had to be grouped with which one. The finding suggests implications for vocational English material development, vocabulary learning and teaching, and research on textbook analysis.