The data in Table 5 below are from a population-based cohort study of an exposure E and a disease outcome D. The data have been stratified by status of a factor Z, and were collected over a one-year period. Table 5 Z=1 D=1 D=0 E=1 120 2090 E=0 98 900 Z=0 D=1 D=0 E=1 135 875 E=0 503 1500 27. Calculate the unconfounded risk difference for the total effect of E on D. Briefly explain your method for doing so