Given information below, calculate the average treatment effect among the untreated. Joint probability D =0 D = 1 Marginal S = 1 0.22 0.18 0.40 S = 2 0.22 0.28 0.50 S = 3 0.06 0.04 0.10 Marginal 0.50 0.50 Potential outcome D =0 D = 1 S = 1 E[Y IS] = 3 E[Y' | S] = 4 E[Y' - Yo S] = 1 S = 2 E[Y' IS] = 6 E[Y' |S] = 6 E[Y' - Yo S] = 0 S = 3 E[Y' S] = 9 E[Y' | S] = 8 E[Y1 - Yo S] = -1