Actual Illinois Map

Last Monday I talked about Illinois redistricting and sure enough a map has come out.

The media immediately jumped all over it. I've seen predictions on the web that this is a 12-6 Democratic map, possibly even 13-5.

So let's see how these changes would've impacted Republicans in 2008:

At first glance it doesn't look good. Four districts Republicans currently hold would flip over, although one that's expected to flip IL-10 would not.

The problem here is that Democrats won those four districts in 2008. So increasing Democrats in their district won't change things. We need to look at those five freshmen Republicans. How will they do in 2012? The first question is how much the 6 Republican congressmen who ran for re-election improved.

So 2010 was worth an average of 6.7%. Now 2012 is unlikely to be as tough as 2008, even in Illinois, so this is probably worst case scenario. Adjusting for the drop off and the change in their districts we end up with:

Argh! It is ugly. Maybe we should write off IL-8, 10, 11, and 17.

Not so fast. Let's go back up one chart. There was one dramatically larger improvement, Aaron Schock. Schock was the only one who was a new representative. Just like these five. This isn't unexpected. Intuitively we know that an incumbent does better than someone running for an open seat. But how much better?

Let's go back to 2002-2004. They had very similar national congressional results. Republicans got 52.4% of the vote in 2002 and 51.4% in 2004. The President was running for re-election in 2004, same as he is this year. I'm going to stick with races that were competitive in 2002, since the races we're looking at all were. I've excluded a few that had unusual circumstances (e.g. the candidate ran unopposed in 2004, Texas redistricting). Here's what we come up with:

Well, that's all over the board, isn't it? We do have 36% of the elections where the incumbent goes up by 9.0% or more, but also 3 elections where the incumbent went down. On average, however, incumbents went up 6.3%. So let's take this +6.3% and deduct the 5.7% decrease that the Republicans (without Schock) got.

That's certainly much more interesting, isn't it? Here, every race but one is competitive.

There are a lot of things we don't know about 2012. Will Obama once again win 63.8% of the vote in Illinois? If he does worse statewide, he'll likely do worse in each district, resulting in the district being more Republican. Will these freshmen all run in their current districts? Will they have quality challengers? Are they the incumbent who does a lot better in their second election or one that does worse?

There are a lot of factors that'll go into 2012 results. These districts might be the easy wins for Democrats people are predicting. That's just not set in stone. The Democrats will have to hit something that right now looks like it has a 50%-60% chance of happening all four times. That's statistically very difficult.