The graph below contains the information from a cohort study investigating the association smoking (exposure) and kidney disease (outcome - case). The research team also examined cumulative arsenic exposure in drinking water as an effect modifier. 160 140 -.. Low arsenic 143 exposure 120 High arsenic 100 exposure Rate of Kidney Disease per 1000 80 - - 0 75 60 55 40 32 20 O No Smoking (A-) Smoking (A+ )