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. 672). 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