My previous analysis, some 2.5 weeks ago, showed control of the Senate in the hands of the Republicans with a 70.5% probability and a mean of 51 seats. We have had a plethora of new polls since then, and we have seen a big change at the top of the ballot.
Now, after 100,000 simulated elections, Democrats have a Senate majority 28,826 times, there were 34,688 ties, and Republicans control the Senate 36,486 times. If we presume the VP will be a Democrat (and this seems very likely), Democrats have a 63.5% probability of controlling the Senate and Republicans, a 36.5% probability of controlling the Senate.
Where have the changes come?
First, is Illinois, where we didn’t have much polling before. A new poll has Tammy Duckworth (D) leading Mark Kirk (R) by an astonishing 14.4% in a four-way race. Illinois moves from 81.1% chance to a 99.8% chance of electing the Democrat.
In Indiana, where Democrat Evan Bayh is up against Republican Todd Young, we have but a single current poll that has Bayh up +1%. The previous poll had Bayh up +4%, so the Democrat’s chances have dropped from 77.2% to 56.2%–just about a tie.
We have no new polling in Missouri, where Democrat Jason Kander is challenging the incumbent Sen. Roy Blunt (R). But two older polls have dropped out and we are left with one Emerson poll with Kander at +2%. Blunt’s chances have dropped from 97.4% to 35%.
New Hampshire has been a back-and-forth race between Democrat Maggie Hassan and Sen. Kelly Ayotte (R). Ayotte led in the last analysis with a 56.5% probability of winning. Five polls have aged out and four new one have been completed. Now she is up to 68.6% probability.
In North Carolina, Democrat Deborah Ross is challenging Sen. Richard Burr (R). This race has seen a significant shift in the polling and Burr’s 91% probability of winning has changed to a 61.1% probability for Ross.
In Oregon, Sen. Kate Brown (D) is defending her seat against Republican Bud Pierce. The only polling in the last analysis was small and had her up +8%. A new poll has Brown up +15%. Consequently her chances have gone up to 100%.
Oops…I got the gubernatorial candidate names in the Senate file. So it is Mark Callahan (R) versus Sen. Ron Wyden (D). The poll numbers are correct, however, so the only polling in the last analysis was small and had him up +8%. A new poll has Wyden up +15%. Consequently his chances have gone up to 100%.
Pennsylvania is another state where an incumbent is endangered, with Democrat Katie McGinty leading Sen. Pat Toomey (R). Previously she had a 78.3% probability of taking the seat. The loss of five polls and the gain of seven new polls have shifted this a little, and now KcGinty has a 68.7% chance
Here is the distribution of Senate seats from the simulations:*
This graphs shows the probability of at least each number of seats controlled by the Democrats:*
- 100000 simulations: Democrats control the Senate 63.5%, Republicans control the Senate 36.5%.
- Average ( SE) seats for Democrats: 49.9 ( 1.1)
- Average (SE) seats for Republicans: 50.1 ( 1.1)
- Median (95% CI) seats for Democrats: 50 (48, 52)
- Median (95% CI) seats for Republicans: 50 (48, 52)
Expected outcomes from the simulations:
- Democratic seats w/no election: 35
- Independent seats w/no election: one
- Republican seats w/no election: 30
- Contested Democratic seats likely to remain Democratic: nine
- Contested Republican seats likely to remain Republican: 18
- Contested Democratic seats likely to switch: one
- Contested Republican seats likely to switch: six
This table shows the number of Senate seats controlled for different criteria for the probability of winning a state:* Safe>0.9999, Strong>90%, Leans>60%, Weak>50%
|Threshold||Safe||+ Strong||+ Leans||+ Weak|
This table summarizes the results by state. Click on the poll number to see the individual polls included for a state.
@ Current party in office
& An older poll was used (i.e. no recent polls exist).
*Analysis assume that the two independent candidates will caucus with the Democrats.
Details of the methods are given in the FAQ.