| |||||||||||||||||||||||||||||||||||||||||||
 |
The 2018 Midterm Elections | ||||||||||||||||||||||||||||||||||||||||||
|
Probability Model For the past 18 years, LatestPollResults has offered an unbiased, statistically-based probability analysis of the Presidential, Senate, and House elections. We calculate each candidate's probability of winning in each race. With these individual race probabilities, we calculate the odds for every possible combination of outcomes and each party's overall probability of winning. Our probabilities are not future projections. They represent the probabilities assuming the election were held today. Here is a summary of our current probabilities for the Senate and House: | |||||||||||||||||||||||||||||||||||||||||||
Probability of Democratic Control | |||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||
|
Senate Recap After the 2016 election, Republicans held a 52-48 edge over Democrats. Currently, Republicans hold a 51-49 edge. This year there are 35 Senate seats which are up for election, 26 will be defended by Democrats and 9 by Republicans; 42 Republicans and 23 Democrats are not up for re-election. With 35 seats, there are 2^35, over 34 billion, possible combinations of outcomes. As you can see from the above probabilities, at this time, the odds that the Democrats will win enough seats to take control of the Senate are apparently low. Poll-based odds:
Since 2010, we've been analyzing the Senate by using data from the latest poll for each race to calculate each candidate's probability of winning the race.
With these individual race probabilities, we calculate the odds for every possible combination of outcomes and each party's overall probability of winning.
Our poll-based analysis has correctly pointed to the winning party in 2010, 2012, 2014 and 2016.
Here is the current probability distribution for our poll-based analysis:
 Market-based odds:
In 2016, we began market-based analysis of the Electoral College and the Senate by using data from individual contract pricing at the Predictit.org marketplace, to calculate each candidate's probability of winning.
From these individual race probabilities, we calculate the odds for every possible combination of outcomes and each party's overall probability of winning.
For 2016, the market-based odds on election day pointed to a 65.8% chance the Democrats would control the Senate, with the help of a 50-50 tie based on the 87.6% market probability they would win the Presidency.
The Democrats had a 41.2% chance of outright control (51+ seats.)
Obviously, the market-based system missed the mark for the Presidency and the Senate.
Here is the current probability distribution for our market-based analysis:
 Analyst-based odds:
For 2018, we're beginning our analyst-based analysis using the analyst ratings from The Cook Political Report, Inside Elections, Sabato's Crystal Ball, and Real Clear Politics.
Each offers a qualitative rating for every seat in the Senate and House and in each state during a Presidential election year.
Seats are rated as "Safe" or "Solid," "Likely" or "Favored," or "Lean," or "Tilt" (Inside Elections only) for the Democrat or for the Republican or rated as a "Tossup."
For each analyst, using their final ratings for 2010, 2012, 2014, and 2016,
we evaluated the percentage accuracy for each rating for both the Senate and House and use this percentage as the probability for each analyst's current ratings.
With these individual race probabilities, we calculate the odds for every possible combination of outcomes and each party's overall probability of winning control of the Senate as well as the House.
We've been tracking each analyst's probabilities on a daily basis since late March:
 House Recap After the 2016 election, Republicans held a 241-194 edge over Democrats. Currently, Republicans hold a 236-193 edge over Democrats. With all 435 seats up, there are 2^435 possible combinations of outcomes. This number is 131 digits long and dwarfs the number of atoms in the universe ... by 50 orders of magnitude! Since not every competitive district is polled, we cannot use our poll-based method for analyzing the House. Similarly, not every competitive district has market pricing available, so we cannot use our market-based method either. We are analyzing the House using our analyst-based method. We've been tracking each analyst's probabilities on a daily basis since late March:  | |||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||