Chapter 12.5, Problem 12.47ACI

Arsenic in groundwater. Refer to the Environmental Science & Technology (January 2005) study of the reliability of a commercial kit to test for arsenic in groundwater, Exercise 12.16 (p. 701). Recall that you fit a first-order model for arsenic level (y) as a function of latitude (x₁), longitude (x₂), and depth (x₃).

1. a. Write a model for arsenic level (y) that includes first-order terms for latitude, longitude, and depth, as well as terms for interaction between latitude and depth and interaction between longitude and depth.
2. b. Use statistical software to fit the interaction model, part a, to the data. Give the least squares prediction equation.
3. c. Conduct a test (at α = .05 ) to determine whether latitude and depth interact to affect arsenic level.
4. d. Conduct a test (at α = .05 ) to determine whether longitude and depth interact to affect arsenic level.
5. e. Practically interpret the results of the tests, parts c and d.