It's difficult to turn on CNBC, read any newspaper article on oil prices, or listen to other discussions of the topic of oil prices without hearing this theory: really, it's the decline in the dollar that's responsible for the rise in oil prices. "They" advance two reasons for this: first, dollar-denominated oil traded on the NYMEX must go up equal to the amount that the dollar goes down, or it's actually losing value. Second, the belief that the dollar is losing its footing as the world's reserve currency is causing a flight from dollars to commodities and other hedges against a falling dollar. Lots of words, but very little data is usually provided to back this up. I decided to put together a little graph that cuts right to the heart of the matter:
Figure 1: US Dollar Index (Bottom) and NYMEX Crude Oil (Top) contracts concurrent price charts
So, let's look at two periods: before about March 10, 2008, and after about March 10, 2008.
Before March 10, 2008, there was a general (though not very convincing) correlation between dollar movement and oil price movement. We need to remember that correlation does not necessarily equal causation here, even if there are rational explanations for a potential causal mechanism. This correlation extends back into 2007 (not shown--chart begins about Jan. 1st, 2008).
After March 10, 2008, there is not a correlation between dollar movement and oil price movement. The dollar has remained relatively steady and constrained within a relatively narrow trading channel. During this same time period the price of oil experienced one of the most dramatic increases in history.
Problem: How can we infer causation from the rough correlation from 2007 to March 10th, 2008 between dollar decline and oil increase if the two data sets become uncorrelated between March 10th and the present? There are possible answers to this question--possibly because there's a lag time between dollar decline and the move to oil and other commodities, possibly because there was some new countermanding force propping up the dollar since March 10th, or something else entirely. The point isn't that there's no explanation for this--the point is that the break in correlation itself defeats any rational use of correlation as the sole basis for asserting causality. At a minimum, we'd need to perform a three-factor analysis here and see if, then, we can derive a continuing correlation--say between an identifiable fed action data set, the dollar index, and crude oil. To my knowledge, no one in the media who has been bandying about the dollar-oil theory has done that. That seriously undercuts the argument that oil price rises are due to dollar decline, in whole or in part. As with any scientific experiment to determine causality, the non-correlation between March 10th and the present must be explained or the entire dollar-oil theory falls apart. I realize that it might be beyond the attention span/sound-bite requirement for most media to discuss this, but it certainly could be addressed in a newspaper or magazine article. I have seen neither. I'll keep thinking about it, but if there are any theories that people would like put to the test, please comment!