Republicans Are Expected to Gain 42 Seats

Based on polling data released over the last five months, Republicans are expected to gain between 25 and 60 seats in the U.S. House of Representatives (with a 90 percent level of credibility). According to the model, the most likely outcome is about a 42 seat gain by Republicans, down slightly from the previous estimate. Such an electoral accomplishment would be sufficient to unseat the Democratic Party from majority status in the lower chamber. The Republican gains would also represent the largest electoral landslide since 1994.

A statistical model that analyzes the results of 15 independent polling firms indicates that Republicans lead Democrats by a margin of 1.3 percent on the so-called generic ballot--a measure of national voter preference between the two major congressional caucuses. This figure is slightly smaller compared to the April estimate of 1.8 percent. The May estimate implies that, if the election were held today, Republicans would achieve a 11 seat majority over Democrats--a very modest advantage.

Over the next six months, I will update this model and estimate Republican electoral gains. The charts below will provide the change in voter preferences over time, along with the probability distribution for the number of seats gained by Republicans on election day. See my April 30, 2010 post for an explanation of my methodology.

Senate Prediction: Republicans Gain Five Seats

Using a similar methodology as my model for the U.S. House, I predict that the Republicans will gain five seats in the U.S. Senate. Here is a seat-by-seat summary (margin of victory in parentheses; party turnover in italics):

Safe Democratic, 6 Seats (15 percent+) :
Boxer (CA)
Inouye (HI)
Mikulski (MD)
Schumer (NY-A)
Gillibrand (NY-B)
Leahy (VT)

Strong Democratic, 4 Seats (5.0 -15.0 percent):
IL (Burris)
Wyden (OR)
Murray (WA)
Feingold (WI)

Weak Democratic, 3 Seats (0.0 - 5.0 percent):
CT (Dodd)
Reid (NV)
PA (Spector)

Weak Republican, 4 Seats (0.0 - 5.0 percent):
Bennet (CO)
DE (Kaufman)
FL (LeMieux)
NH (Gregg)

Strong Republican 6 Seats (5.0 - 15 percent):
McCain (AZ)
Grassley (IA)
IN (Bayh)
MO (Bond)
Burr (NC)
OH (Voinovich)


Safe Republican 13 Seats (15.0 percent+):
Shelby (AL)
Lincoln (AR)
Crapo (ID)
Isakson (GA)
Murkowski (AK)
KS (Brownback)
KY (Bunning)
Vitter (LA)
ND (Dorgan)
Coburn (OK)
DeMint (SC)
Thune (SD)
UT (Bennett)

A Projection for the Senate: Republicans Gain Five Seats

Using a similar methodology as my model for the U.S. House, I have constructed predictions for the Senate. Here is a seat-by-seat summary (margin of victory in parentheses; party turnover in italics):

Safe Democratic, 6 Seats (15 percent+) :
Boxer (CA)
Inouye (HI)
Mikulski (MD)
Schumer (NY-A)
Gillibrand (NY-B)
Leahy (VT)

Strong Democratic, 5 Seats (5.0 -15.0 percent):
CT (Dodd)
IL (Burris)
Wyden (OR)
Murray (WA)
Feingold (WI)

Weak Democratic, 2 Seats (0.0 - 5.0 percent):
Reid (NV)
Specter (PA)

Weak Republican, 3 Seats (0.0 - 5.0 percent):
Bennet (CO)
DE (Kaufman)
NH (Gregg)

Strong Republican 8 Seats (5.0 - 15 percent):
McCain (AZ)
Lincoln (AR)
FL (LeMieux)
Grassley (IA)
IN (Bayh)
MO (Bond)
Burr (NC)
OH (Voinovich)


Safe Republican 12 Seats (15.0 percent+):
Shelby (AL)
Crapo (ID)
Isakson (GA)
Murkowski (AK)
KS (Brownback)
KY (Bunning)
Vitter (LA)
ND (Dorgan)
Coburn (OK)
DeMint (SC)
Thune (SD)
Bennett (UT)