1. Novis BH, Marks IN, Bank S, Louw JH. Incidence of Crohn's disease at Groote Schuur Hospital. S Afr Med J 1975;49:693–7.
2. Wright JP, Marks IN, Jameson C, Garish JA, Burns DG, Kottler RE. Inflammatory bowel disease in Cape Town, 1975–1980. S Afr Med J 1983;63:226–9.
3. Wright JP, Froggatt J, O'Keefe EA,et al. The epidemiology of inflammatory bowel disease in Cape Town, 1980–1984. S Afr Med J 1986;70:10–5.
4. O'Keefe EA, Wright JP, Foggat J, Zabow D. A medium term follow-up of Crohn's disease in Cape Town. S Afr Med J 1989;76:139–41.
5. Hill AB. Principles of medical statistics. 8th ed. London: Lancet, 1966:232.