Data from Sweden indicates that there is a strong correlation... Data from Sweden indicates that there is a strong correlation between the number of storks (a type of bird) and the number of babies born. We know that more storks live in the urban areas than in the rural areas.

a) Draw a three-variable diagram to show the relationship between the number of storks, the number of babies born, and region (rural vs. urban).

b) If we control for the effect of region, what will happen to the correlation between the number of stork and the number of babies born?