Where there are more storks, there are more babies. That’s true! The higher the number of storks in an area, the higher the birthrate. Could it be that storks actually do bring babies? Well, no. It...

Where there are more storks, there are more babies. That’s true! The higher the number of storks in an area, the higher the birthrate. Could it be that storks actually do bring babies? Well, no. It turns out that storks tend to inhabit rural areas, and rural areas have higher birthrates than urban areas. That is, an extraneous variable (urban versus rural) is the variable that connects those two causally unrelated variables.