Will the Real Battleground States Please Stand Up?

by Karl Kurtz

Tim Storey, my colleague at NCSL and a leading expert on state legislative elections, and I have had an ongoing discussion over the last several elections about how best to decide which states are "battleground" states--the ones in which there is a real chance of party control changing hands.

Tim's method is to highlight the chambers in which the majority party has a margin of 5 or fewer seats and then to add his own political intelligence to determine if these states are really in play.  The results of his analysis are published in Top 10 Election Battlegrounds.  He discussed these results at length during a press conference at NCSL's Annual Meeting.

My argument is that picking out the chambers with margins of 5 or fewer seats does not take into account the size of the legislative chamber or the number of seats that are up for election.  To take an extreme case, let's pretend that Republicans have a four-seat majority in the New Hampshire House (in reality their margin is a whopping 92 seats) just as they actually do in the Alaska Senate.  Leaving out the possibility of ties, this means that the Democrats would have to have a net gain of three seats to gain control of each of these chambers. With 400 seats up for election, our pretend New Hampshire Democrats would have to make a net gain of only less than 1% of the seats (3 out of 400) to take control. But in Alaska, with only half the Senate up for election (10 seats), party control would have to change in at least 30% of the seats for the chamber to switch--a much tougher hurdle.

So my solution is to take into account the size of the legislative chamber by defining the battleground states as the ones in which one party has a majority of 55% or less.  In those states, I create an index of the likelihood of a switch in party control by dividing the number of net seat changes needed for a switch by the number of seats up for election.  I then rank them from lowest (greatest likelihood of a switch) to highest.

To find out more about battleground states, continue reading after the jump.

The effect of my method compared to Tim's is that more chambers--especially ones with large numbers of seats up for election like the Michigan and Pennsylvania houses--fall into the battleground category.

For his part, Tim buys into my argument that the statistical measure should be a percentage of seats rather than a flat number.  But he counters that if you don't add political intelligence to the mix, then the statistical likelihood doesn't mean much.  I agree with him, so he and I have collaborated on a new measure of the battleground states that we call the "switch index." View our switch index online.

In the end, what difference does it make?  Not much, but it makes my political scientist's heart feel better that we have added a little bit more rigor to the analysis.

In the next 3 weeks of election season--and especially on election night and the days afterward--check back with The Thicket.  This post is an example of how we plan to integrate our coverage of the elections between StateVote 2006 and The Thicket.  The StateVote Web page will contain our best information on election outcomes at any given time; in The Thicket we will provide commentary and interesting tidbits that we pick up as we do our coverage.