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Election Update: How Our House Forecast Compares With The Experts’ Ratings

FiveThirtyEight’s Election Updates are back! This will be a regular feature in which we track the race for the House (and, eventually, Senate and governors’ offices) using our forecasts to highlight particularly interesting trends and races.

According to the latest run of the “Classic” version of our model, Democrats have a 3 in 4 chance of taking over the House; their average gain is 34 seats. This hasn’t changed too much since we launched the forecast last Thursday, when Democrats’ average gain was 35 seats. However, there have been some changes under the surface as we’ve made improvements to the model. You can find an overview of those here, and we’ll be updating our “how the forecast works” page soon with more detail.

But since this is our first Election Update, today I want to focus on the bigger picture. Our model joins the political discourse as only one of many predictors of the fall’s elections, and three of the most respected election handicappers are our friends over at the Cook Political Report, Inside Elections and Sabato’s Crystal Ball. Historically, their race ratings have a strong record of accuracy — so much so that we have a whole iteration of our forecast, the “Deluxe” version, that exists solely to incorporate their ratings. So, while we remain devoted to hard data above all, it’s always good to see how our bloodless, but systematic, approach matches up with more subjective, but expert, opinions.

And, generally, they do. As of Tuesday, Cook, Inside Elections, Crystal Ball and FiveThirtyEight’s Classic forecast all had the same race rating for 322 out of the 435 House races.1 FiveThirtyEight agreed with or was only one category removed from Cook in 424 races, Crystal Ball in 423 races and Inside Elections in 410 races. Our mileage may vary in whether to call a GOP-favored race “lean Republican” or “likely Republican,” but, generally, our different techniques are leading mostly to the same results.

But there are also some differences. For example, FiveThirtyEight’s forecast is a tad more bullish on Democrats’ chances overall than the three major handicappers. If you assign probabilities to their race ratings,2 Cook’s and Sabato’s ratings both imply a Democratic gain of 29 seats, while Inside Elections’s compute out to a Democratic gain of 23. (Our forecast, remember, currently projects an average Democratic gain of 34 seats.)3

The Democratic tail is also longer in our Classic forecast — that is, the model gives a greater chance than the experts do that a blue wave turns into a tsunami and Democrats pick up a ton of seats, like 60 or 70. That’s because the model rates fewer seats as truly safe for Republicans — or “solid” in FiveThirtyEight parlance — than the experts do.

How four forecasters see the House battleground

The number of congressional districts rated in each category by each handicapper as of 9:30 a.m. on Aug. 22, 2018

Rating FiveThirtyEight Cook Political Report Inside Elections Sabato’s Crystal Ball
Solid/safe Republican 136 152 164 147
Likely Republican 53 25 26 35
Lean Republican 17 27 12 16
Toss-up* 15 29 38 34
Lean Democratic 15 9 5 11
Likely Democratic 9 12 5 12
Solid/safe Democratic 190 181 185 180
Total competitive 109 102 86 108

* Includes Inside Elections’s “tilt” races.

Competitive races are those in the categories of “likely Republican” through “likely Democratic.”

By a small margin, our forecast also places more seats in the “solid Democratic” category and all the competitive categories combined (between “likely Republican” and “likely Democratic”).

Who will be right? We honestly don’t know! We’re still 11 weeks out from the election, and things are still subject to a lot of change. The long tails in our forecast reflect that, but it’s worth noting that there’s no real way for the qualitative ratings to communicate uncertainty. The bottom line is that, in the big picture, and in terms of average seat gain, all the major forecasters agree: Democrats are mild favorites to take back the House.

Check out all the polls we’ve been collecting ahead of the 2018 midterms.



Footnotes

  1. FiveThirtyEight’s versions of the race ratings are derived from the probability the model assigns a Democratic or Republican win in each district. If there’s a 95 percent chance or higher that one party will win a race, we consider it “solid” for that party. If a party’s chances are at least 75 percent but less than 95 percent, it’s a “likely” race for that party. If a party’s chances are at least 60 percent but less than 75 percent, it’s a “lean” district. And if both parties have less than a 60 percent chance of winning, it’s a “toss-up” district.

  2. Assuming FiveThirtyEight’s probabilities for each category of rating also apply to Cook, Inside Elections and Crystal Ball. It’s important to note that the three handicappers don’t endorse any formal conversion between race rating and chance of winning.

  3. All the figures in this paragraph are as of Wednesday at 11 a.m. Eastern.

Nathaniel Rakich is FiveThirtyEight’s elections analyst.

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