Introducing the SVI- Swing Voter Index
OK, we’re all familiar with PVI, that magic index of the partisan lean of a geopolitical division that tells us, on “average”, the party lean of said geopolitical divison. A useful figure, but PVI leaves a lot unexplained. Let’s look at my home state of Minnesota’s statewide and congressional district (CD) PVIs for a start:
CD PVI
1 R+5
2 R+2
3 D+1
4 D+14
5 D+26
6 R+12
7 R+12
8 R+4
State D+1
Conventional wisdom tells us that anything beyond an R+5 is a lost cause, so most Democratic Party leaders write off CD6 and CD7 and consider CD1 and CD4 long shots. But every single one of these CDs was won by at least one democrat in 2018! WTH? So lets add some more data, the worst and best percentages of the vote earned by a statewide candidate for each party in 2018 and the swing vote in each CD:
CD PVI Dem Range Rep Range Swing Voter %
1 R+5 42%-54% 42%-52% 16%
2 R+2 46%-59% 38%-48% 16%
3 D+1 50%-63% 35%-45% 15%
4 D+14 61%-71% 25%-33% 14%
5 D+26 73%-82% 15%-20% 12%
6 R+12 36%-48% 48%-58% 16%
7. R+12 36%-48% 48%-59% 16%
8 R+4 43%-54% 43%-51% 14%
State D+1 49%-60% 36%-45% 15%
First, some cautions about the data- PVI is an average of the last two presidential election results, giving us a sample of two and we did a lot better in 2012. The 2018 election in Minnesota gave us a sample of six statewide races, and more data is usually better. Looking at the low end of each party’s percentage of the vote gives us a fair measure of each party’s base. Our democratic base exceeds 50% in CD3, and even more so in CD4 and CD5, suggesting that CD3 has shifted democratic while CD4 and CD5 have been safe democratic districts for decades. Despite have double digit R+ PVIs, CD6 and CD7 are winnable by democrats, proven by Amy Klobuchar winning both and Collin Peterson winning CD8. And despite many pundits having put CD1 and CD8 into the “lean republican” category, both parties have almost identical base votes in the 42-43% range.
Adding together each party’s base vote and subtracting from 100% gives the “swing” vote and our Swing Voter index. As expected, the Swing Voter Index shows the lowest percentage of swing voters in the strongest democratic CDs and the highest percentage of swing voters in the more republican leaning but still competitive CDs.
I’m still developing this Swing Voter Index (SVI) and debating how much more data to add from congressional races and 2016 and maybe earlier results to hopefully more accurately gauge the size of the swing vote, and I want to scale down to legislative districts too. So comments are welcome, even if you think me the fool…
Sassy Democrat 