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2. Royal College of Physicians of London: Smoking and Health Now London, Pitman 1971.
3. Fisher, R. A.: Smoking: The Cancer Controversy. Edinburgh: Oliver and Boyd 1959.
4. Kröning, F.: Naturwissenschaften45, 73 (1958).
5. Berkson, J.: J. Amer. Stat. Assoc.53, 28 (1958).