This prediction has been replaced/updated with this one.
I have added new models to my previous prediction of a Republican gain of 61 seats in the House.
First, one must predict the vote totals for each party. Currently, RCP’s average of the “Generic Congressional Vote” shows Republicans winning 49.3% to 41.6%. However, you clearly see two outliers, one to the upside (Gallup LV Lower Turnout) and one to the downside (Newsweek). Excluding those two gives you a pretty tight pack varying from +7 to +11, a small 4 point range versus the huge 20 point range if you include the two extreme polls. Based on these five closely-packed polls, Republicans lead Democrats 49.8% to 40.6%. Eliminating the undecideds (if they have not decided by now, they are unlikely to vote) gives a two-party vote total of 55.1% for the Republicans and 44.9% for the Democrats.
I now have three models to convert vote totals to House seats.
40-year model: Regression of House seats vs. vote total for every election since 1968.
8-year model: Regression of House seats vs. vote total for every election since 2002. Because of the increase in partisanship and computerized gerrymandering, there are now many more safe seats.
1994 & 2006 model: In these two mid-term elections, control of the House switched sides against an unpopular President. The same will likely occur this year.
The models produce the following results:
40-year model: Republicans win 268 House seats, gain of 90 seats.
8-year model: Republicans win 247 House seats, gain of 69 seats.
1994 & 2006 model: Republicans win 253 House seats, gain of 75 seats.
Taking a simple average of the three, I now predict the Republicans will win 256 House seats, a gain of 78 seats.
* Again, I will update these numbers as new polls come in. But if you look at the polls on RCP over the last month, Republicans have been consistently in the lead by 8 or 9 points. Barring some late breaking change in this election, I don’t expect these number to change much. But who know how accurate the polling is this year? We won’t know for certain until November 2.