This is principally arrived at through deductive and inductive logic and parsimony within the limits and domains of science and related rational presuppositions. It is to be remembered that experiments and observations generate data, and in some point there would be a need for interaction between data and theory, which leads the methodology beyond the realm of deductive rationality to collection of data and their interpretation in such a manner that the whole affair can be replicated (Wilson 1952).
John Snow is famous as an epidemiologist who first demonstrated conclusively that cholera is actually caused by microorganisms, and he deductively established that these organisms affect the human beings through transmission by food or water. His epidemiologic work is now considered as the classic reference of modern epidemiology and has been termed by Frost to be a “nearly perfect model” (Morabia 2001). Snow’s work on cholera epidemic in London would not have been possible without the scientific disease surveillance methodologies enacted by Farr, which indicated the importance of water supply in South London. Based on the data collected by Farr, Snow could reach a conclusion about the causation of cholera epidemics in London. Based on the distribution of mortality data from cholera, it was possible for him to locate the households that were getting comparatively cleaner water and hence lesser incidence of the disease and related death rates (Morabia 2001).
The necessity of a controlled experiment in order to implicate the water supply in the London cholera epidemic in 1848-1849 was understood by both, but Snow got an intellectual leap from the data collected by Farr, through the simple method of grouping the households based on a definition of exposure to the causative agent. Despite the thought of controlled experiment