Arsenic in groundwater. Refer to the Environmental Science

& Technology (Jan. 2005) study of the reliability of a commercial kit to test for arsenic in groundwater, Exercise 12.23

(p. 700). Recall that you fit a first-order model for arsenic level (y) as a function of latitude (x1), longitude (x2), and depth (x3) to the data. Conduct a residual analysis of the data.

Based on the results, comment on each of the following:

a. assumption of mean error = 0

b. assumption of constant error variance

c. outliers

d. assumption of normally distributed errors

e. multicollinearity