An analysis of state head-to-head polls in Senate races suggests that Republicans would most likely control the Senate if the election was to be held today. Democrats have made small improvements since my previous analysis in July.
After 100000 simulated elections, Democrats have a Senate majority 1239 times, there were 10566 ties), and Republicans control the Senate 88195 times. Democrats have a 11.8% probability of controlling the Senate and Republicans have a 88.2% probability of controlling the Senate. This is only up slightly from the previous analysis. Where Democrats have gained is in the number of expected seats, going from 48.2 (on average) to 48.5. The median number of seats remains at 48.
A few states warrant comment.
The Arizona race has gone in Sen. John McCain’s (R) favor. He was at a 76% chance in July; now he is nearly at 100%. That said, the polling show great variability, so Democrat Ann Kirkpatrick may not be down for the count just yet.
Nothing has changed in Illinois, in the seat held by Republican Mark Kirk. Democrat Tammy Duckworth only has a 38% chance of winning, but the polling is old and (possibly an outlier). Illinois may well be a pick-up, but we don’t have good, recent polling to say so.
Last July, U.S. Representative Baron Hill (D) withdrew from the Indiana Senate race to make room for former U.S. Senator Evan Bayh (D). That changed the nature of the race. The state is now widely considered a Democratic pick-up.
Missouri was nearly a toss-up in July. Now it is solid for Republican Roy Blunt. Democrat Jason Kander only wins 22 the 100,000 simulated elections.
In Nevada, Democrat Catherine Cortez Masto was leading Republican Joe Heck with a 67% probability of winning in July. Alas, the polling since then has favored Heck, and the Republican now has a 91% of winning an election now. Still, most of the polls are extremely close.
New Hampshire’s incumbent Republican Kelly Ayotte has been in the fight for her life against Democrat Maggie Hassan. In July, the race was tied up. And, the fact is, Hassan leads in most polls. But one strong recent poll gives Ayotte the edge with a 78% probability of winning right now.
In Ohio, Democrat Ted Strickland has been slowly losing ground to incumbent Sen. Rob Portman (R). The graph says it all:
Pennsylvania was red in the previous analysis. But Sen. Pat Toomey (R) has been slipping to Democrat Katie McGinty, and the Democrat now has an 87% chance of winning now.
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 11.8%, Republicans control the Senate 88.2%.
- Average ( SE) seats for Democrats: 48.5 ( 0.9)
- Average (SE) seats for Republicans: 51.5 ( 0.9)
- Median (95% CI) seats for Democrats: 48 (47, 50)
- Median (95% CI) seats for Republicans: 52 (50, 53)
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: 21
- Contested Democratic seats likely to switch: one
- Contested Republican seats likely to switch: three
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 |
|---|---|---|---|---|
| Safe Democrat | 44 | |||
| Strong Democrat | 3 | 47 | ||
| Leans Democrat | 1 | 1 | 48 | |
| Weak Democrat | 0 | 0 | 0 | 48 |
| Weak Republican | 0 | 0 | 0 | 52 |
| Leans Republican | 2 | 2 | 52 | |
| Strong Republican | 6 | 50 | ||
| Safe Republican | 44 |
This table summarizes the results by state. Click on the poll number to see the individual polls included for a state.
| # | Sample | % | % | Dem | Rep | ||
|---|---|---|---|---|---|---|---|
| State | @ | polls | size | Dem | Rep | % wins | % wins |
| AL | 0 | 0 | (0) | (100) | |||
| AK | 0 | 0 | (0) | (100) | |||
| AZ | 4 | 2737 | 44.7 | 55.3 | 0.0 | 100.0 | |
| AR | 1& | 601 | 36.3 | 63.7 | 0.0 | 100.0 | |
| CA | 2 | 1093 | 100.0 | 0.0 | 100.0 | 0.0 | |
| CO | 2 | 1581 | 58.4 | 41.6 | 100.0 | 0.0 | |
| CT | 1 | 872 | 61.7 | 38.3 | 100.0 | 0.0 | |
| FL | 11 | 7702 | 47.1 | 52.9 | 0.0 | 100.0 | |
| GA | 3 | 1511 | 43.1 | 56.9 | 0.0 | 100.0 | |
| HI | 0 | 0 | (100) | (0) | |||
| ID | 0 | 0 | (0) | (100) | |||
| IL | 1& | 658 | 49.1 | 50.9 | 37.8 | 62.2 | |
| IN | 3 | 1386 | 54.7 | 45.3 | 99.4 | 0.6 | |
| IA | 5 | 3411 | 45.2 | 54.8 | 0.0 | 100.0 | |
| KS | 1 | 454 | 38.1 | 61.9 | 0.0 | 100.0 | |
| KY | 1 | 440 | 43.2 | 56.8 | 2.0 | 98.0 | |
| LA | 1 | 794 | 34.6 | 65.4 | 0.0 | 100.0 | |
| MD | 1 | 618 | 68.1 | 31.9 | 100.0 | 0.0 | |
| MO | 5 | 4079 | 46.5 | 53.5 | 0.0 | 100.0 | |
| NV | 4 | 2191 | 48.0 | 52.0 | 8.9 | 91.1 | |
| NH | 10 | 6514 | 49.3 | 50.7 | 22.0 | 78.0 | |
| NY | 2 | 1642 | 69.8 | 30.2 | 100.0 | 0.0 | |
| NC | 8 | 5409 | 48.2 | 51.8 | 3.5 | 96.5 | |
| ND | 0 | 0 | (0) | (100) | |||
| OH | 8 | 5527 | 45.1 | 54.9 | 0.0 | 100.0 | |
| OK | 0 | 0 | (0) | (100) | |||
| OR | 1 | 403 | 55.1 | 44.9 | 92.7 | 7.3 | |
| PA | 12 | 7900 | 50.9 | 49.1 | 87.2 | 12.8 | |
| SC | 1 | 941 | 38.4 | 61.6 | 0.0 | 100.0 | |
| SD | 0 | 0 | (0) | (100) | |||
| UT | 1 | 678 | 27.9 | 72.1 | 0.0 | 100.0 | |
| VT | 2 | 1086 | 67.6 | 32.4 | 100.0 | 0.0 | |
| WA | 1 | 430 | 60.5 | 39.5 | 99.9 | 0.1 | |
| WI | 6 | 3939 | 55.6 | 44.4 | 100.0 | 0.0 |
@ 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.
What happens in the PA race if the poll window is narrowed to the current presidential poll window time period you employ? Some of the 12 polls included are several weeks old, and the last six polls have split 3-3. Thank you.
Sloppy,
Using a one-month polling window barely changes anything.
Pennsylvania now has 3,815 “votes” from 6 polls. McGinty takes 50.6% of votes, Toomey 49.4%. McGinty would be expected to take an election now with 71.1% probability (down from 87.2%).
Overall: Mean # Dem seats drops by 0.2 from 48.5 to 48.3. Median is unchanged. Probability of Democrats taking the Senate increases slightly from 11.8% to 13.9%.
The slight increase in probability for Dems taking the Senate is an artifact of there simply being fewer polled individuals when a one month poll window is used. This increases uncertainty and pushes both winning probabilities toward 50%.