The Republicans are about 85% likely to take control of the U.S. Senate in January, 2015. This is going to happen, because the Democrats are going to win Blue States and the Republicans are going to win Red States. And, the Republicans are likely going to win two crucial Purple States (Iowa and Colorado). This election is not wave or a disaster for either party, but pretty much as should be expected. The most likely outcome is going to be the Democrats controlling 47-8 seats to the Republican 52-3.
The Democratic path to victory is very simple; they need to capture both New Hampshire and North Carolina, which are likely, and then three additional states of the five in play. The runoff system makes it very unlikely they will win in Georgie and Louisiana. And, I do not think Kansas’ Orman is going to make himself the swing vote with a 49 Democratic senate. Why would he do that if he can switch back in 2017 with seniority when the Democrats recapture the senate?
There is a possibility of a systematic polling bias against the Democrats (i.e., the Democrats will over-perform polls on Election Day). Nate Silver seems to think I am wrong (although the post is very long and does not address me directly, so it is hard to say for sure). He believes that the bias in 2012 is an historical anomaly. His argument is that states tend to break towards their fundamentals (i.e., Democratic states polls are biased against Democrats and Republican states polls are biased against Republicans). The problem is that he runs a regression with data from 1998 to 2012 and includes presidential polling along with senatorial. First, in 1997 the response rate for random digit dialing was still 36%, versus <9% in 2012. While I applaud the use of added observations, including time before the technical issues appeared for pollsters is a mistake that will smooth all treatment effects. Second, presidential polling is going to swamp senatorial polling. Not only in size, but in stability and accuracy. Presidential elections have more stable voter turnout.
Knowing there was an issue in 2012, I have no doubt that the pollsters will try to correct for any bias, but I believe it is likely that there will still be some bias against Democrats. First, with shifts in both coverage and non-response error moving fast it is not easy to correct for what happened in two or four years ago. Baseline data used for corrections is already obsolete (i.e., reliable lists of cell-phone only versus landline/cell phone are not updated fast enough!) and simply correcting for the error of four years ago is also obsolete (i.e., any correlations from four years ago are already wrong). This group of pollsters may under or over correct, but it is hard to see how they would be systematic unbiased. Further, they are technically very conservative people, so under-correcting is just more likely. Second, many pollsters are not knowledgeable enough to do that and will not bother. This group of pollsters are likely to favor Republicans.
Note: I had a very interesting early morning phone call today with Sam Wang of Princeton, so I expect he may touch on some of the same topics about bias today as well.
Any potential systematic polling bias, that favors the Democrats, will only get them Colorado and possibly Iowa; putting them at 49 seats. Colorado is most likely, because, with high population movement and Hispanic population, it is susceptible to bias. High population movement, young people with cell phones, leads to coverage error that favors Republicans. Hispanic population lead to non-response error, as Democratic Hispanics are less likely to answer English polls as Republican Hispanics. Iowa is the next most likely, as a Democratic leaning purple state shares some of the same attributes. It is less likely that Alaska or Georgia are going to be heavily hit by bias, as both states are much less susceptible. Kansas does not have a Democratic challenger!