1. Berkson, J., and Gage, R. P. (1950). Proc. Mayo Clin., 25, 270.
2. Diseases of the Heart;Friedberg, C.K.,1949
3. Gilchrist, A. R., and Tulloch, J. A. (1956). Scot. med. J., 1, 1.
4. Principles of Medical Statistics;Hill, A.Bradford,1955
5. Jones, A. M. (1955). Brit. med. J., 2, 1613.