Page 47 - The Principle of Economics

minivan comes before the baby, but we wouldn’t want to conclude that the sale of minivans causes the population to grow!
There is no complete set of rules that says when it is appropriate to draw causal conclusions from graphs. Yet just keeping in mind that cigarette lighters don’t cause cancer (omitted variable) and minivans don’t cause larger fam- ilies (reverse causality) will keep you from falling for many faulty economic arguments.
CHAPTER 2 THINKING LIKE AN ECONOMIST 45