While there are still 10 months until the 2018 elections, we can start to predict the results now using a variety of factors. In this article, I will discuss how I predict seats, my personal formula, and the predicted results of the 2018 Senate Election.

How I Predict Seats, and My Personal Formula

When making seat predictions, I take 6 things into account: the most recent Presidential election results by state, the second-most recent Presidential election results by state, the most recent Senate election results for each state, a composite of generic ballot polls, a composite of Trump approval ratings, and incumbency.

For all election results used, I find the difference between the Republican and Democrat vote percentages. If the state voted for a Democrat, a positive number is used. If the state voted for a Republican, a negative number is used. For generic ballot polls, I take the FiveThirtyEight composite and find the total Dem lean. For approval ratings, I take the FiveThirtyEight composite and find the total disapproval lean. For incumbency, I give 5 points to the incumbent party.

Each factor is weighted differently based on how long ago the factor was obtained, and how accurate the factor can be considered. My personal formula weights the factors as follows:

2012 Presidential Results by State: 10%

2012 Senate Results by State: 20%

2016 Presidential Results by State: 15%

Generic Ballot: 35%

Trump Approval Rating: 20%

Incumbency: 5 points in either direction or 0 points if no incumbent

You can view my spreadsheet with all of my data here.

*For Tennessee, I gave the Democrat running an advantage equal to an incumbency advantage because the candidate, Phil Bredesen, won the Tennessee governor’s race in a landslide and is very popular.

Predictions

When I ran all the numbers through my formula, I got the total Dem lean of a Senate seat. I used the following guidelines for ratings:

Between -5 and 5 lean: Tossup

Between -10 and 10 lean: Lean

Between -17 and 17 lean: Likely

Other: Safe

Using this rating system, I got the following results:

Total Democratic Seats: 48

Total Republican Seats: 48

Total Tossups: 4

Here’s the map:

And here’s the map with no tossups:

In conclusion, my 2018 predictions show a tossup Senate race, with Democrats leading in 3 out of the 4 tossups.

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