One thousand simulations of midterm vote reveal … 51-seat average GOP gain

To sum up, first we generated 1,000 simulations of the national vote. Then, we applied each of the 1,000 simulated national outcomes to each congressional district, noting the party of the “winner.” For each of the 1,000 simulated outcomes of the national vote, we project the partisan division of the 435 congressional districts.

The figure below displays the range of simulated results. As can be seen from the predominance of red bars, the Republicans win the majority of seats in 79% of the trials. On average, the Republicans win 229 seats, 23 more than the Democrats and 11 more than the 218 needed for a majority. However, the simulations yield considerable variation, with a 95% confidence interval of 176 to 236 Republican seats.