14 thoughts on “Swing State Project PVI”

  1. I like the idea of a PVI based on just one election, but I would propose focusing a bit more effort on calculating CPVIs for the 04 and 08 elections for comparison… I would think that 2004 may have been a more normal election year and that any changes in 2008 will have been from the obvious Obama effect…

  2. I’m having a hard time interpreting this spreadsheet without seeing the PVI right next to the SVI.

    I understand, in these elections it shouldn’t make much of a difference, but let’s test that assumption.

    Thanks!

    -j

  3. I have long held the exact same qualms mentioned by the original post.  I don’t think PVI is utterly useless, but I think your explanation of SVI would be far more helpful.  I would really love to see this move forward.

  4. You should consider modifying the formula to take two most recent elections into account as Cook does, instead of only most recent election as your spreadsheet shows.  Using two elections smooths outs bumps in election results that can occur because particular candidates played well or poorly in particular regions.  It is also more consistent with the current Cook PVI formula which uses two years and thus both more familiar to all and more likely to be accepted.

    The formula for the Cook PVI is as follows:

    Cook PVI = (Bush’s 2000 two-party vote share in congressional district – Bush’s 2004 two-party vote share nationally) + (Bush’s 2004 two-party vote share in congressional district – Bush’s 2004 two-party vote share nationally)/2.  Postive numbers are Republican PVIs and negative numbers are Democratic PVIs (or you could get the same reults using the Democratic candidate’s numbers and then positive numbers would be D PVIs and negative numbers would be R PVIs).

    The entire problem with the Cook PVI is that it compares 2000 state results with 2004 national results.  The USA as a whole should have a PVI of 0.0.  But, by comparing 2000 state results with 2004 national results (apples to oranges) it screws things up and, in fact, the USA as a whole had a PVI of R+0.8 for 2005-2008 (you can run the numbers yourself using the above formula if you don’t believe me).  Using this same formula to calculate new PVIs after 2008 elections results in the USA as a whole having a PVI of D+2.5.  This is totally screwy and defeats the purpose of the Cook PVI which is to show how much a congressional district is more democratic or republican than the nation as a whole.  The formula fix to correct this problem is simple:

    Proposed new PVI = (Kerry’s 2004 two-party vote share in particular congressional district – Kerry’s 2004 two-party vote share nationally) + (Obama’s 2008 two-party vote share in congressional district – Obama’s 2008 two-party vote share nationally)/2.  Positive numbers are Democratic PVIs and negative numbers are Republican PVIs.

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