Chris Bowers discusses the implications of the chart above, which appears to show the price of gasoline (mapped inversely so that the line goes down when the price of gas goes up) exerting a dominant influence on George W. Bush's popularity. I was super-impressed the first time I saw that chart, but now I'm not so sure. Aside from the fact that gasoline has generally gotten more expensive and Bush generally gotten less popular, are we really seeing a correlation here? There must be any number of quantities that have also generally moved in one direction during the relevant time period.
Consider the quality of the basketball teams fielded by the New Jersey Nets. Like Bush, they were at their best in the season immediately following 9/11 and have been in slow but steady decline since then. But the Nets aren't exercising a causal influence on Bush's popularity. What's more, I think the price of gas is being demarcated in nominal terms here, which is clearly the wrong way to do it.
Matthew Yglesias is a former writer and editor at The Atlantic.