OZY's Exclusive Election Model: Bet on Republicans to Hold the Senate

OZY's Exclusive Election Model: Bet on Republicans to Hold the Senate

Why you should care

A Democratic House takeover with room to spare remains likely, but new polls show that Dems face a very slim chance for Senate victory.

Storm clouds are brewing for Republicans nationwide, according to the political forecast. President Donald Trump’s approval rating is slumping, and Democrats are showing steady enthusiasm. And yet … the GOP’s Senate fortunes improved last week.

OZY’s exclusive midterm predictions model, in partnership with Republican data and technology firm 0ptimus, projects the GOP to hold 52 Senate seats, with an 85.6 percent chance of holding at least 50 seats to retain their majority. The House projection is steady from last week: Democrats have an 88.6 percent chance of taking over the chamber, with a projected 227 seats, to Republicans’ 208. We crunched more than 100 factors that helped predict past elections, with some extra weighting for unique aspects of this political year, to produce these forecasts. For more on how these numbers were derived, scroll down to the bottom of this story. For more exclusive election coverage, subscribe to our Midterms in a Minute newsletter.

Democrats’ advantage in the national political environment continues to rise, to 9.3 percentage points, up from 8.8 last week. “Despite the national environment, Republicans seem to be picking up steam in the Senate,” says Alex Alduncin, data scientist at 0ptimus. This week’s batch of public polling showed them “tied or leading in Florida, Missouri, Arizona, Indiana and Tennessee, among others. These are the states that will very likely determine control of the chamber.”

Republicans have an overwhelmingly favorable Senate map to work with, as Democrats are defending 10 seats where Donald Trump won in 2016 — including five where Trump won by at least 18 percentage points. Republicans, by turn, are only defending one state that Hillary Clinton won (Nevada). Democrats’ incredibly narrow path to a Senate majority must include a pickup in at least one of three deep red states: Tennessee, Mississippi and Texas. While Lone Star state Democrat Beto O’Rourke has generated rock star crowds and bountiful friendly national press coverage, Sen. Ted Cruz still has a 70.2 percent chance of victory, our model shows.

On the House side, the OZY/0ptimus model shows 24 House races as tossups — meaning one party has a chance of victory between 40 and 60 percent. Newly added battlegrounds this week include Georgia’s 7th Congressional District in the Atlanta suburbs (where incumbent Republican Rep. Rob Woodall has a 59.42 percent chance of victory), southeastern Arizona’s 2nd District (where Republican Lea Marquez Peterson has a 40.39 percent chance of holding the open seat) and New Jersey’s 3rd District (where Democrat Andy Kim, whom OZY profiled last year, has a 42.22 percent chance of knocking off Republican Rep. Tom MacArthur in the Philadelphia suburbs).

In addition to our extensive on-the-ground coverage of races across the U.S. this year, OZY wanted to build a better product to analyze the national political picture — given the failure of such forecasts in the past. So we decided to team up with Washington-based 0ptimus, a Republican firm that developed an unbiased, nonpartisan prediction model so it could show its clients in the worlds of both politics and finance where the winds were blowing.

0ptimus’ data team created and tested countless models, crunching publicly available data against past results in House and Senate races. They take into account more than 100 variables, including past vote totals, generic ballot surveys of which party voters prefer in Congress, the unemployment rate, fundraising data and public polling. The firm developed an artificial intelligence system to “smartly” average together several models to create the strongest prediction numbers for the 2018 elections, always automatically testing against past elections to assess quality. You can read more about the 0ptimus methodology here.

Given the unique factors of 2018, we asked 0ptimus to tweak its calculations, adding additional weight to:

  • The number of small donations — a sign of energy for candidates from Trump to Alexandria Ocasio-Cortez.
  • Gender — women are doing exceptionally well this year, and we expect that trend to continue.
  • Trump’s approval rating — as he hangs over the political and media scene with a heavier presence than past presidents.

Meanwhile, we asked 0ptimus to reduce the weight for:

  • Candidate ideology — their calculations rewarded more moderate candidates, while we think this election year is all about firing up the base.
  • Outside money — as OZY has reported, advertising is less persuasive coming from a super-PAC than from a candidate.

Because 0ptimus averages several models, for us they introduced a new Bayesian model to the mix that included Trump approval, gender and unitemized donations, while removing one that included ideology and independent expenditures. The result is the numbers we update for you each week.

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