1. Campbell, H. 1965. Changes in Mortality Trends, England and Wales, 1931–61. National Center for Health Statistics Analytical Studies No. 3. Washington.
2. McKeown, T. 1964. The next forty years in public health. Popul.Stud.17, 269.
3. Morris, J. 1962. The Uses of Epidemiology. London and Edinburgh. Livingstone.