Suppose that model (XY, XZ, YZ) holds in a 2 X 2 X 2 table, and the common XY conditional Log odds ratio at the two levels of Z is positive. If the XZ and YZ conditional log odds ratios are both positive or both negative, show that the X)’ marginal odds ratio is larger than the XY conditional odds ratio. Hence, Simpson’s paradox cannot occur for the XY association.