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2. Crohn's disease in the central area of Spain;Garcia,1981
3. Epidemiology of Crohn's disease and ulcerative colitis: etiologic implications;Gilat;Isr J Med Sci,1979
4. Fall in the incidence of Crohn's disease;Kyle;Gut,1980
5. Newer concepts of IBD epidemiology;Mendeloff,1982