12.127 Arsenic in groundwater. Refer to the Environmental Science & Technology (January 2005) study of the WELLS reliability of a commercial kit to test for arsenic in groundwater, Exercise 12.16 (p. 710). Recall that you fit a first-order model for arsenic level (y) as a function of latitude (x1), longitude (x2), and depth (x3) to data saved in the file. 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 WAGAP 12.132 Agreeableness, gender, and wages. Refer to the Journal of Personality and Social Psychology (Feb. 2012) study of on-the-job agreeableness and wages, Exercise 12.107 (p. 760). Recall that the researchers modeled mean income, E(y), as a function of both agreeable- ness score (x1) and a dummy variable for gender (x2 = 1 if male, 0 if female). Use the data saved in the file to analyze the residuals of the model, E(y) = Bo+ Bx1 + B (x1) + B3x2 What model modifications, if any, do you recommend? ASWELLS (Data for first and last five wells shown) WELLID LATITUDE LONGITUDE DEPTH ARSENIC 10 23.7887 90.6522 14 23.7886 90.6523 30 23.7880 90.6517 59 23.7893 90.6525 125 85 23.7920 90.6140 150 55458 60 331 302 193 232 19 7353 23.7949 90.6515 40 48 7357 23.7955 7890 23.7658 90.6515 30 172 90.6312 60 175 7893 23.7656 90.6315 45 624 7970 23.7644 90.6303 30 254