A. Show that Cov(X, Y + Z) 5 Cov(X, Y) 1 Cov(X, Z). b. Let X1 and X2 be quantitative and verbal scores on one aptitude exam, and let Y1 and Y2 be corresponding scores on another exam. If Cov(X1, Y1) = 5, Cov(X1, Y2) = 1, Cov(X2, Y1) = 2, and Cov(X2, Y2) = 8, what is the covariance between the two total scores X1 + X2 and Y1 + Y2.

Researchers are conducting experiments to determine the role of alcohol in the development of depression. after the study is complete, they determine that the relative risk of developing depression is 1.55 with a 95 % ci of 1.2 -1.9. each group is then divided into nonsmokers and smokers. the relative risk for the nonsmokers is 1.12 with a 95% ci of 0.87-1.37. the relative risk for the smokers is 1.7 with a 95 % cl of 1.5-1.9. what type of bias may affect this study? a. procedure bias b. recall bias c. selection bias d. confounding e. lead-time bias