Which of the following is an accurate description of simpson's paradox?

a. when groups of data are aggregated, an association can get stronger because of a confounding variable. that confounding variable is usually the number of observations in the different groups of data.
b. when groups of data are combined, an association can get stronger because of a lurking variable. that lurking variable is usually the number of observations in the different groups of data.
c. when groups of data are combined, an association can reverse direction because of inaccurate data. that inaccurate data usually concerns the number of observations in the different groups of data.
d. when groups of data are separated, an association can get stronger because of a lurking variable. that lurking variable is usually the number of observations in the different groups of data.
e. when separate groups of data are combined, an association can reverse direction because of a lurking variable that was lost when the different groups of data were lumped together.