4.12              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 (micro- grams per liter), the latitude (degrees), longitude

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

.

.

.

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

SPSS output for Exercise 4.11

(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.