We all know that correlation doesn't prove causation anyway, but the issue I'd like to raise about the purported tight link between the price of gasoline and George W. Bush's approval rating is that it's hardly clear to me that there's even a correlation here beyond the basic fact that Bush's approval rating has generally gone down since 9/11 and oil prices have generally gone up.
Consider, if you will, the detail to the left. This shows the data from September of 2005 to September of 2007, a period during which the final price of gas was very close to the initial price, but Bush's approval rating fell by a small but clear amount. Nothing about eyeballing this chart would lead you to conclude that gas prices were driving changes in Bush's approval rating. Sometimes the two indexes move in the same direction and sometimes they move in different directions. But since each index can only go in one of two directions, one would expect totally unrelated quantities to move in the same general directions about half the time.
All that said, obviously we do know that economic conditions are one of several factors that impact presidential approval ratings and that gasoline prices are an important determinant of people's assessments of their economic well-being. We also know that sometimes gas prices go up because of events (Katrina, for example) that independent make the president look bad. But the initial formulation of the gas-approval chart is meant to show a very tight link between the two quantities and it seems to me that the link just isn't there.
Matthew Yglesias is a former writer and editor at The Atlantic.