Arsenic in groundwater. Refer to the Environmental Science & Technology (Jan. 2005) study of the reliability of a commercial kit designed to test for arsenic in groundwater, presented in Exercise 12.23 (p. 700). You fit a first-order model for arsenic level (y) as a function of latitude, longitude, and depth. On the basis of the model statistics, the researchers concluded that the arsenic level is highest at a low latitude, high longitude, and low depth.

Do you agree? If so, find a 95% prediction interval for arsenic level for the lowest latitude, highest longitude, and lowest depth that are within the range of the sample data.

Interpret the result.