Update, Saturday: with two new surveys in Alaska, one showing a tie and the other showing a Begich (D) lead, the predicted Senate Meta-Margin is D+0.0%, a perfect tossup. Statistically this is not different from the minuscule difference yesterday…but it does emphasize how closely fought the battle for control is. To see more, click on the seat graph at the right or the Meta-Margin graph.
Now that Greg Orman (I-KS) has a median lead of 1.5%, the Senate Meta-Margin has gone to R+0.4%. For those who are new, let me explain what this means.
The Meta-Margin is defined as “how much swing would it take to create a perfect toss-up for control.” In other words, if polls swung by a scant 0.4% across the board, then a 50R, 50D/I split would become about as equally likely as a 51R, 49D/I split. Recall that across-the-board midterm polling errors (i.e. in the Meta-Margin) are typically 2-3%, and are five times as large as presidential-year polling errors. I would say we do not know who will control the Senate!
Here is another way to think about it: Democrats and Independents are reasonably assured of winning 45 seats. A relatively likely outcome (the mode) is to add Hagan (NC), Shaheen (NH), Orman (KS), and Nunn (GA), to make 49. At this point, if Republicans lose Alaska, Arkansas, Colorado, Iowa, or Kentucky, then they will be left with 50 seats. Of course, with 10 races having margins within 4%, this is just one of 2^10=1024 likely combinations. The Princeton Election Consortium’s meta-analysis considers them all.