=+21. Water hardness. In an investigation of environmental causes of disease, data were collected on the annual mortality rate (deaths per 100,000) for males in 61 large towns in England and Wales. In addition, the water hardness was recorded as the calcium concentration (parts per million, or ppm) in the drinking water. Here are the scatterplot and regression analysis of the relationship between mortality and calcium concentration, where the dependent variable is Mortality.

Variable Coeff SE(Coeff)

Intercept 1676.36 29.30 Calcium -3.226 0.485 R-squared = 42.9%

s = 143.0 with 61 - 2 = 59 degrees of freedom 2000 1800 1600 1400 1200 30 60 90 120 Calcium (ppm)

Mortality (deaths/100,000)