Poll Analysis: Senate Race Update
Sunday, September 7, 2008 at 10:01 pm
| Senate Democrats* | Senate Republicans |
| 100.0% probability of a majority | 0.0% probability of a majority |
| Mean of 57 seats | Mean of 43 seats |

Time for a Senate race update. Wait, actually, the update is way overdue. There were no state head-to-head polls of any type today, so what the heck….
The previous analysis, way back on August 26th, showed control of the Senate firmly in the hands of the Democrats with an expected 56.5 seats to the Republican’s expected 43.5 seats. There have, of course, been numerous Senate state head-to-head polls released since then. The bottom line is, the Democrats improve their position very slightly.
Today after 100,000 simulated elections, Democrats still are guaranteed to control the Senate. Now they have an expected 56.8 seats to the Republican’s 43.2 seats. That’s a gain of almost 1/3 of a seat.
Compared to the previous analysis, Democrats lose some prospects in Alaska (from 100% to 69%), Colorado (from 99% to 72%), and Minnesota (from 15% to 8%). But they gain some in Missouri (from 2% to 7%), North Carolina (from 17% to 86%) and Oregon (from 1% to 16%).
Here is the distribution of Senate seats from the simulations:*

Notice that this is the first time the magic 60 seats shows any probability mass at all on this graph. It is a very small mass, but there it is.
This graphs shows the probability of at least each number of seats controlled by the Democrats:*

- 100000 simulations: Democrats control the Senate 100.0%, Republicans control the Senate 0.0%.
- Average ( SE) seats for Democrats: 56.8 ( 1.0)
- Average (SE) seats for Republicans: 43.2 ( 1.0)
- Median (95% CI) seats for Democrats: 57 (55, 59)
- Median (95% CI) seats for Republicans: 43 (41, 45)
Expected outcomes from the simulations:
- Democratic seats w/no election: 37
- Independent seats w/no election: two
- Republican seats w/no election: 26
- Contested Democratic seats likely to remain Democratic: 12
- Contested Republican seats likely to remain Republican: 17
- Contested Democratic seats likely to switch: none
- 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 |
|---|---|---|---|---|
| Safe Democrat | 51 | |||
| Strong Democrat | 3 | 54 | ||
| Leans Democrat | 3 | 3 | 57 | |
| Weak Democrat | 0 | 0 | 0 | 57 |
| Weak Republican | 0 | 0 | 0 | 43 |
| Leans Republican | 2 | 2 | 43 | |
| Strong Republican | 6 | 41 | ||
| Safe Republican | 35 |
This table summarizes the results by state. Click on the poll number to see the individual polls included for a state.
| # | Sample | Percent | Percent | Democrat | Republican | ||
|---|---|---|---|---|---|---|---|
| State | @ | polls | size | Democrat | Republican | % wins | % wins |
| Alabama | 1& | 445 | 34.8 | 65.2 | 0.0 | 100.0 | |
| Alaska | 1 | 475 | 51.6 | 48.4 | 68.8 | 31.2 | |
| Arkansas | 0 | 0 | (100) | (0) | |||
| Colorado | 1 | 437 | 51.9 | 48.1 | 71.7 | 28.3 | |
| Delaware | 0 | 0 | (100) | (0) | |||
| Georgia | 1& | 470 | 46.8 | 53.2 | 16.5 | 83.5 | |
| Idaho | 1 | 426 | 42.3 | 57.7 | 1.2 | 98.8 | |
| Illinois | 1& | 470 | 64.9 | 35.1 | 100.0 | 0.0 | |
| Iowa | 1& | 460 | 63.0 | 37.0 | 100.0 | 0.0 | |
| Kansas | 1 | 571 | 34.9 | 65.1 | 0.0 | 100.0 | |
| Kentucky | 1& | 585 | 43.4 | 56.6 | 1.1 | 98.9 | |
| Louisiana | 1& | 475 | 58.9 | 41.1 | 99.7 | 0.3 | |
| Maine | 1& | 475 | 42.1 | 57.9 | 0.8 | 99.2 | |
| Massachusetts | 1& | 425 | 65.9 | 34.1 | 100.0 | 0.0 | |
| Michigan | 1 | 516 | 68.6 | 31.4 | 100.0 | 0.0 | |
| Minnesota | 1& | 580 | 45.9 | 54.1 | 8.2 | 91.8 | |
| Mississippi | 1 | 475 | 45.3 | 54.7 | 7.3 | 92.7 | |
| Mississippi | 1& | 455 | 35.2 | 64.8 | 0.0 | 100.0 | |
| Montana | 0 | 0 | (100) | (0) | |||
| Nebraska | 1& | 470 | 36.2 | 63.8 | 0.0 | 100.0 | |
| New Hampshire | 2 | 1223 | 55.3 | 44.7 | 99.5 | 0.5 | |
| New Jersey | 1& | 659 | 61.0 | 39.0 | 100.0 | 0.0 | |
| New Mexico | 1 | 644 | 55.4 | 44.6 | 97.5 | 2.5 | |
| North Carolina | 3 | 2031 | 51.7 | 48.3 | 86.2 | 13.8 | |
| Oklahoma | 1& | 615 | 36.6 | 63.4 | 0.0 | 100.0 | |
| Oregon | 1& | 470 | 46.8 | 53.2 | 16.5 | 83.5 | |
| Rhode Island | 1& | 460 | 78.3 | 21.7 | 100.0 | 0.0 | |
| South Carolina | 1& | 466 | 37.1 | 62.9 | 0.0 | 100.0 | |
| South Dakota | 1& | 579 | 64.2 | 35.8 | 100.0 | 0.0 | |
| Tennessee | 1& | 445 | 33.7 | 66.3 | 0.0 | 100.0 | |
| Texas | 1 | 450 | 42.2 | 57.8 | 1.0 | 99.0 | |
| Virginia | 1 | 902 | 63.2 | 36.8 | 100.0 | 0.0 | |
| West Virginia | 0 | 0 | (100) | (0) | |||
| Wyoming | 0 | 0 | (0) | (100) | |||
| Wyoming | 0 | 0 | (0) | (100) |
@ Current party in office
& An older poll was used (i.e. no recent polls exist).
*Analyses assume that independent Senators Sanders and Lieberman continue to caucus with the Democrats.
Details of the methods are given in the FAQ.
The most recent analysis in this and other elections can be found from this page.






