Here’s a great case of a third variable causing a correlation between two things that are themselves unrelated.
“We know the wireless-only population is more likely to binge-drink, more likely to smoke, more likely to be be uninsured,” said Stephen Blumberg, a senior scientist at the CDC’s
Younger adults are more likely to have only a cellphone, not a landline. And younger people are more likely to binge-drink, etc. It’s not the cellphone that causes binge drinking, and not binge drinking that causes you to drop your landline.