T R5.30. Hard water 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 anal- ysis of the relationship between mortality and calcium concentration. Dependent variable is Mortality R-squared = 43% 5 = 143.0 with 61 - 2 = 59 degrees of freedom Variable Coefficient SE(Coeff) Intercept 1676 29.30 Calcium -3.23 0.48 2000 -+. 1800 1600 Mortality (deaths/100,000) 1400 1200 - 30 60 90 120 Calcium (ppm) a) Is there an association between the hardness of the water and the mortality rate? Write the appropriate hypothesis. b) Assuming the assumptions for regression inference are met, what do you conclude? c) Create a 95% confidence interval for the slope of the true line relating calcium concentration and mortality. d) Interpret your interval in context