Analyze each of the following arguments in terms of the variation of the “phenomena” to show how they follow the pattern of the method of concomitant variation:

In Finland, heart attacks occur more frequently in the eastern part of the country than in the western and southern parts. Researchers seeking to explain these differences concluded that they “cannot be explained by individual lifestyle or by genetic factors.” How, then, can they be explained? A study led by Dr. Anne Kousa, of the Geological Survey of Finland, examined heart attacks that occurred in 18,946 men, ages 35 to 74, in three different years. The researchers then correlated the incidence of heart attack in these populations with the level of water hardness—as measured by the presence of minerals in the water—in their communities. The study found that the degree of water hardness correlated directly with a lowered risk of heart attack. Drinking water rich in minerals appears to play a role in reducing heart disease.
—Journal of Epidemiology and Community Health, January 2004