The Oil Drum

Stuart and I have been emailing back and forth regarding his post on modeling state gsp using vmt as an independent variable.

Paula, both here and on her blog, correctly suggested that education should also be considered as an independent variable. So, what I did was pull together some data on % college educated for each state and include it in with the data Stuart had already collected...and then I conducted a multivariate regression on the data, which is presented below.  That regression allows us to find out what the effects are for all of these independent variables on gsp/cap after controlling for the effects of the other variables.  This allows to get a better picture of what's going on (though we lose the visual facility that Stuart had with his bivariate graphs).  Much more under the fold.

So, what's the takeaway?  Stuart's right: states with higher vmts have lower gsp/cap, even after controlling for education and population density.

This is one of those analyses that I started with a firm opinion: I thought I knew where it was going. And then it went somewhere else and ended in a bit of a mystery. Details of my puzzlement below the fold.

The graph to the right shows Gross State Product/Capita (source: BEA, 2003) plotted versus Vehicle Miles Traveled/Capita (source: FHWA, 2003 table VM-2) for 48 of the 50 US states. Click the graph to enlarge it.