1. Inflammatory bowel-disease and domestic hygiene in infancy;Gent;Lancet,1994
2. Shivananda S, Leonard-Jones J, Logan R, et al. Incidence of inflammatory bowel disease across Europe: is there a difference between north and south? Proceedings of the Maastricht meeting of the EC Study on Inflammatory Bowel Disease, Maastricht, Netherlands. April 26–27, 1996.
3. World Health Organization annual epidemiological vital statistics,1960
4. United Nations demographic yearbook,1971
5. United Nations demographic yearbook,1981