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.