Arsenic in groundwater. Environmental Science and Technology (January 2005) reported on a study of the reliability of a commercial kit to test for arsenic in groundwater. The field kit was used to test a sample of 328 groundwater wells in Bangladesh. In addition to the arsenic level (micrograms per liter), the latitude (degrees), longitude (degrees), and depth (feet) of each well was measured. The data are saved in the ASWELLS file. (The first and last five observations are listed below.)
(a) Write a first-order model for arsenic level (y) as a function of latitude, longitude, and depth.
(b) Fit the model to the data using the method of least squares.
(c) Give practical interpretations of the β estimates.
(d) Find the model standard deviation, s, and interpret its value.
(e) Interpret the values of R2 and R2a.
(f) Conduct a test of overall model utility at α = .05.
(g) Based on the results, parts d-f, would you recommend using the model to predict arsenic level (y)? Explain.