Nakajima, K., Nagao, K., Tai, T., Kobayashi, H., Hara, H., Miura, K., & Ishii, N. (2010). Duration of sexual intercourse related to satisfaction: Survey of Japanese married couples. Reprod Med Biol.

Nakajima, Koichi, Koichi Nagao, Toshihiro Tai, Hideyuki Kobayashi, Hiroshi Hara, Kazukiyo Miura, and Nobuhisa Ishii. "Duration of Sexual Intercourse Related to Satisfaction: Survey of Japanese Married Couples." Reprod Med Biol 2010.

Nakajima, Koichi, et al. "Duration of Sexual Intercourse Related to Satisfaction: Survey of Japanese Married Couples." Reprod Med Biol 2010.