Licence: In copyright
Credit: Age incidence in zymotic diseases / by John Brownlee. Source: Wellcome Collection.
Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.
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![[From the Proceedings of the Royal Philosophical Society of Glasgow.] Age Incide?ice in Zymotic Diseases. (A contribution from the Sanitary and Social Economy Section). By John Browni.ee, M.A., M.D., (Glasg.), D.P.H. (Camb.), Physician Superintendent, City of Glasgow Fever Hospital, Belvidere- [Read before the Society, 34th Fehruar)-, 1904.] The subject of this paper is a consideration of the meaning of the statistics of infectious diseases, as they occur at different ages, in the light of the mathematical developments of the theory of probability which have been divised in recent years, especially by Professor Karl Peanson. The needs of astronomers and surveyors long ago made the adoption of some means of reconciling discordant observations a practical necessity. It early came to be generally recognised that if an observation were made a certain number of times with equal care, and with equally perfect instruments, the most probable value of the quantity observed is the arithmetical mean or average of the values given by the ob.servations. From this, what is commonly called the normal probability curve, was deduced as a necessary consequence. The normal probability curve, which is figured in diagram I., is the geometrical expression of the frequency with which any error of definite magnitude may be expected to occur in a number of observations. It is symmetrical about the middle line, which indicates that positive and negative errors are equally likely to occur. The ordinate or vertical distance of any point on this curve from the base line decreases in value as the error increases in magnitude, thus large errors occur with great infrequency, while small ones are much more numerous. The example which is most commonly chosen to illustrate the application of this law to practical problems is taken from rifle shooting. Given a good shot, using a rifle without bias, the atmosphere being clear and steady, out of a given number of shots bull’s eyes will constitute the most numerous group ; inners will follow, then outers, while misses will be the rarest of all. As many shots will fall to the right of the bull’s eye as fall to the left, and as many above as](https://iiif.wellcomecollection.org/image/b24931007_0005.jp2/full/800%2C/0/default.jpg)
