REFERENCES
- Anderson, R. P., Bonchek, L. I., Grunkemeier, G. L., Lambert, L. E. & Starr, A. J. Surg. Res. 1974, 16, 224–230
- Bergman, L. & Krause, U. In: Bergman, L. (ed.) Crohn's disease. A study of epidemiology, aetiology and therapy. Thesis. Uppsala 1976
- Bradford Hill, A. pp. 220–236 in Principles of Medical Statistics. The Lancet Limited, London. 1961
- Brill, C. B., Klein, S. F. & Kark, A. E. Ann. Surg. 1969, 170, 766–774
- DeDombal, F. T., Burton, I. & Goligher, J. C. Brit. J. Surg. 1971, 58, 805–816
- DeDombal, F. T., Burton, I. & Goligher, J. C. Gut 1971, 12, 519–527
- Fausa, O., Nygaard, K. & Elgjo, K. Scand. J. Gastroent. in press
- Fielding, J. F., Cooke, W. T. & Williams, J. A. Surg. Gynec. Obstet. 1972, 134, 467–469
- Glotzer, D. J., Gardner, R. C., Goldman, H., Hin-richs, H. R., Rosen, H. & Zetzel, L. New Engl. J. Med. 1970, 282, 582–587
- Greenstein, A. J., Sachar, D. B., Pasternack, B. S. & Janowitz, H. D. New Engl. J. Med. 1975, 293, 685–690
- Havia, T. & Thomasson, B. Acta Chir. Scand. 1972, 138, 844–847
- Janowitz, H. D. J. Chron, Dis. 1975, 28, 63–66
- Korelitz, B. J., Present, D. H., Alpert, L. I., Marshak, R. H. & Janowitz, H. D. New Engl. J. Med. 1972, 287, 110–115
- Krause, U., Bergman, L. & Norlen, B. J. Scand. J. Gastroent. 1971, 6, 97–108
- Lennard-Jones, J. E. & Stalder, G. A. Gut 1967, 8, 332–336
- Nugent, F. W., Veidenheimer, M. C., Meissner, W. A. & Haggitt, R. C. Gastroenterology 1973, 65, 398–402
- Stahlgren, L. H. & Ferguson, L. K. J. Amer. Med. Ass. 1961, 175, 986–989
- Steinberg, D. M., Thompson, A. H., Brooke, B. N., Williams, J. A. & Cooke, W. T. Gut 1974, 15, 845–851
- Williams, J. A. Clin. Gastroent. 1972, 1, 469–489
- Young, S., Smith, J. S., O'Connor, J., Bell, J. R. & Gillespie, G. Brit. J. Surg. 1975, 62, 528–534