Arsenic in groundwater. Environmental Science & 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 were measured. The data are saved in the file. (The first and last 5 observations are listed in the table below.) Well ID Latitude Longitude Depth Arsenic 10 23.7887 90.6522 60 331 14 23.7886 90.6523 45 302 30 23.7880 90.6517 45 193 59 23.7893 90.6525 125 232 85 23.7920 90.6140 150 19 f f f f f 7353 23.7949 90.6515 40 48 7357 23.7955 90.6515 30 172 7890 23.7658 90.6312 60 175 7893 23.7656 90.6315 45 624 7970 23.7644 90.6303 30 254

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 b estimates.

d. Find the model standard deviation, s, and interpret its value.

e. Find and interpret the values of R2 and R2

a. f. Conduct a test of overall model utility at a = .05. g. Based on the results, parts d–f, would you recommend using the model to predict arsenic level (y)? Explain.