What does The Economist’s election model predict for the midterms | The Economist

Key Concepts

• Predictive Modeling: A statistical approach using historical data, polling, and fundraising to forecast election outcomes.
• Generic Ballot Polling: A metric asking voters which party they intend to support in congressional elections, used to gauge national sentiment.
• Midterm Penalty: The historical trend where the party not holding the presidency typically performs well in midterm elections.
• Redistricting/Gerrymandering: The process of redrawing electoral district boundaries, which can significantly impact seat distribution and party advantage.
• Known Unknowns: Variables that are expected to change or be revealed (e.g., primary results, final district maps) that could alter model predictions.

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1. The Economist’s Forecasting Model

The Economist utilizes a comprehensive model to predict U.S. congressional elections. The model integrates:

• Historical Data: Past election results for every district and state.
• Polling Data: National polls, presidential approval ratings, and race-specific polling.
• Special Elections: Results from vacant legislative seat contests.
• Financial Metrics: Fundraising data.

Calibration of Uncertainty: A primary function of the model is to calibrate polling error. It assesses the probability of errors occurring in specific directions and magnitudes across different regions, aggregating these to provide a probabilistic forecast rather than a definitive outcome.

2. House of Representatives Forecast

The model currently gives Democrats a 98% chance of taking control of the House.

• Supporting Evidence:
  • Midterm Dynamics: The party out of power historically gains seats.
  • Generic Ballot: Democrats hold a ~6-point lead.
  • Presidential Approval: The incumbent president’s approval rating is 20 points "underwater" (negative net approval).
  • Map Fairness: Current maps are viewed as reasonably fair, limiting the ability of Republicans to rely on gerrymandering to suppress the popular vote.
• Caveats: The forecast assumes current district maps are final. Potential changes in Virginia or retaliatory gerrymandering in Florida could shift the landscape, though the model suggests these changes would not fundamentally alter the overall outcome.

3. Senate Forecast

The Senate race is described as a "nailbiter" with a 48% chance of a Democratic takeover.

• The Challenge: Democrats need to flip four seats to overcome the Republican advantage (which includes the Vice President’s tie-breaking vote).
• Key Battlegrounds:
  • North Carolina: Likely win for former Governor Roy Cooper.
  • Michigan: A vulnerable open seat currently facing a divisive primary.
  • Maine: The need to unseat Susan Collins, a moderate Republican in a blue state.
  • Deep Red States: Democrats must flip two additional states where Donald Trump won by double digits in the last presidential election.
• Democratic Strengths: Strong candidate recruitment, such as Sherrod Brown in Ohio and Mary Peltola in Alaska, provides potential paths to a 51-seat majority.

4. Variables and "Curve Balls"

The experts identified several factors that could disrupt current predictions:

• Primary Outcomes: The model currently assumes incumbents seeking renomination will succeed. It does not incorporate race-specific polling until both nominees are finalized.
• Redistricting: Ongoing legal challenges and map adjustments remain a significant "known unknown."
• National Political Environment: "Unknown unknowns," such as major global or domestic events, could shift the national mood, potentially erasing the Democrats' 6-point lead on the generic ballot.

Synthesis and Conclusion

The current forecast heavily favors the Democrats in the House due to favorable midterm fundamentals and a strong generic ballot lead. The Senate remains a toss-up, contingent on the party's ability to defend vulnerable seats while simultaneously flipping seats in states that historically lean Republican. The model serves as a probabilistic tool rather than a certainty, with its accuracy heavily dependent on the resolution of primary elections and the finalization of electoral maps. As noted by the experts, while the fundamentals are strong, the "1-in-50" event remains a statistical possibility.