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Theory Development

10. Mechanisms

The mechanisms approach can be understood by taking an epidemiological case as a point of comparison, consider cholera. There were, in the 1850's, strong correlations in London between altitude of residence and incidence of disease. This suggested "miasma" as a mechanism. The real mechanism, however, was water contaminated with the cholera bacillus. Establishing this required a different kind of study, which eventually showed that the correlation was an artifact of pumping methods, not miasma. Applying this kind of reasoning in the social sciences is more difficult, as the mechanisms in question typically involve the mind. But hypotheses about the motivations of individuals may be supported with various kinds of additional evidence, and tests may be devised of some of these hypotheses.

Table 1

Elevation and Cholera Deaths

Elevation of Districts in Feet
Number of Terraces from Bottom
Deaths from Cholera in 10,000 Inhabitants
Calculated Series
Under 20 1 102 102/1 = 102
20-40 2 65 102/2 = 51
40-60 3 54 102/3 = 34
60-80 4 27 102/4 = 26
80-100 5 22 102/5 = 20
100-120 6 17 102/6 = 17
140-160 18 7 102/18 = 6

(Humphreys, N.A. (Editor): Vital Statistics: A Memorial Volume of Selections from the Reports and Writings of William Farr. London , Sanitary Institute, 1885, p. 254-5.)