Our analyst-based analysis uses the qualitative ratings from The Cook Political Report, Inside Elections, Sabato's Crystal Ball, and Real Clear Politics. We adjust their current ratings based upon their historical accuracy.
When Cook, Inside Elections, and Sabato all agree that the seat rating is Safe for the Democrat or for the Republican, they've been 100% accurate in each of the last 5 elections: 2010, 2012, 2014, 2016, and 2018. Here is a summary of each analyst's current ratings for the Senate:
The column % Dem indicates the historical accuracy of the associated rating for each analyst as it relates to the Democrat. For example, when Cook rates a race Lean D, historically, the probability is 100% than the Democrat wins; when Inside Elections rates a race Tilt R, there is a 12.5% chance the Democrat wins.
Note: Inside Elections generally has a lower number of Toss Up ratings due to their additional rating of Tilt which is between Toss Up and Lean. For their final ratings, Sabato moves all Toss Up ratings to either Lean D or Lean R. This provides greater clarity than the other analysts though, Sabato's Lean ratings accuracy suffers as a result versus the other analysts.
From the historical race odds, we calculate each party's overall odds of winning by evaluating every possible combination of outcomes. For the 35 Senate races, there are over 34 billion possible outcomes.
Senate Probability Distribution Cook Political Report:
Senate Probability Distribution Inside Elections:
Senate Probability Distribution Sabato:
Senate Probability Distribution Real Clear Politics: