Following up on the David Nir's diary of the presidential results by congressional district, I decided to look at what the prospects of Democrats regaining the majority in the House of Representatives. The link to David's post is below.
Presidential results by congressional district
The way I went about it was first to look at what the new PVIs were for each of these districts. The PVIs online were still ones based on the 2004 and 2008 results that gave us the PVI for the 2012 races, but now thanks to David's work, we had the vast majority of presidential results by congressional district data (There are still some selected districts, mostly in the Northeast, that we have no presidential number yet). I plugged in those results and now computed the PVI with just the 2008 and 2012 results. Since the PVI is computed by comparing the presidential results in the congressional district vs. the results in the nation as whole, I didn't think that gave as detailed a comparison as I would have liked. I, therefore, computed a "statewide PVI" that compared the presidential results in the congressional district vs. the results in that state as a whole.
For example, if we look at a congressional district that voted for Romney 55-45, the standard PVI would be about R+7 (the difference between 52-47 Obama and 55-45 Romney). But if we then factor in the state that the congressional district is in, we can compare how Republican or Democratic that district is in that state. So, if we look at a 55-45 result in a Utah congressional district (by the way, no Utah congressional district was even close to a 55-45 split) where Romney won the state as a whole by 73%-25%, it is as friendly a Democratic district as you'll find, where as that same 55-45 result in a state like California where Obama carried it by 60-37, is a Republican vote sink.
This "statewide PVI" was determined by taking the standard PVI and subtracting the "lean" of the state. Again, if we take Utah as an example and start with the R+7, which equals -7 (7 points below the Obama/Romney nationwide result) and subtract the statewide "lean" of -26 (Utah was 26 points more in favor of Romney than the nation), we get -7-(-26). If we remember our math from school, subtracting a negative makes a positive so it becomes -7+26 which equals +19. Anything with a positive number is Democratic, negative number is Republican. So, our "statewide PVI" in this hypothetical case is D+19 as that district would be 19 points more Democratic than the state as whole.
Follow me below the "squiggles" for a look at what the 435 congressional districts look like with both PVI and statewide PVI and if it can tell us anything about the possible Republican held districts that can be retaken by Democrats.
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