AN account of some quantitative studies in epidemiology has recently been published in the second edition of my book on the “ Prevention of Malaria ” (Murray), and the Editor of NATURE has asked me to give a general description of them here. The attempts originated in the following manner. Shortly after Anophelines were shown to carry malaria, it was often observed that little apparent correlation could be found between their numbers and the numbers of infected persons in a locality. The observations were always far too scanty to establish any real absence of correlation; but they were used, nevertheless, to support the thesis that the amount of malaria does not depend upon the number of the Anophelines, and that therefore the proposed anti-malarial measure of mosquito reduction (then very unpopular) was useless. For many reasons a trustworthy experimental investigation would have been very difficult and costly, and it was therefore all the more necessary to examine the subject by a carefully reasoned analysis of the relations which must hold between the amount of the disease and the various factors which influence it. My first attempt in this direction was made in an official report on the “ Prevention of Malaria in Mauritius “ (Waterlow and Sons, 1908), and fell into the form of a simple difference equation. This was further developed in the first edition of my book already mentioned, and the subject was at the same time ably attacked by Mr. H. Waite, at the instance of Prof. Karl Pearson, in Biometrika, October, 1910.
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