The Effects of Study Abroad Duration and Predeparture Proficiency on the L2 Proficiency of Japanese University Students: A Meta-Analysis Approach 論文 Akiyo HIRAI・Akiyo Hirai ·2018 ·『日本言語テスト学会誌』 21(0) pp. 102-123 doi:10.20622/jltajournal.21.0_102