1. Yahoo! Answers,
http://answers.yahoo.com/
2. Yahoo! Chiebukuro (in Japanese),
http://chiebukuro.yahoo.co.jp/
3. Nishihara, Y., Matsumura, N., Yachida, H.: Understanding of Writing Style Patterns between Q&A in Knowledge Sharing Community. In: The 22nd Annual Conference of the Japanese Society for Artificial Intelligence (2008) (in Japanese)
4. Kumamoto, T.: Creating an Impression Space to Represent Impressions of News Articles. The Institute of Electronics, Information and Communication Engineers, WI2-2008-35, pp.47–52 (July 18, 2008) (in Japanese)
5. Baayen, R.H.: Nihongo-no goitokusei: Lexical properties of Japanese (Word Imageability). NTT database, vol. 3. Sanseido, Baayen, R. H, Tokyo, Japan (2008) (in Japanese)