HOUSE UPDATE: Republicans Edge Up to a 48 Seat Gain

Based on polling data released over the last seven months, Republicans are expected to gain between 30 and 65 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 48 seat gain by Republicans, up five seats from the previous estimate. If the polling holds steady, Republicans seem to be poised to retake control of the U.S. House of Representatives with the largest electoral landslide since 1994. In fact, based on a Monte Carlo simulation, the Republicans have an 80 percent probability of retaking the House.

A statistical model that analyzes the results of 15 independent polling firms indicates that Republicans lead Democrats by a margin of 1.9 percent on the so-called generic ballot--a measure of national voter preference between the two major congressional caucuses. This figure is somewhat greater than the June estimate of 1.4 percent. The July estimate implies that, if the election were held today, Republicans would achieve approximately an 18 seat majority over the Democrats--a modest, but decisive advantage.

Over the next five 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.

NOTE: I tweaked my charts for the expected margin of majority and the probability distribution for the number of seats gained by Republicans.

Senate Prediction: Republicans to 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, 5 Seats (15 percent+) :
Inouye (HI)
Mikulski (MD)
Schumer (NY-A)
Gillibrand (NY-B)
Leahy (VT)

Strong Democratic, 5 Seats (5.0 -15.0 percent):
Boxer (CA)
CT (Dodd)
IL (Burris)
Reid (NV)
Wyden (OR)

Weak Democratic, 4 Seats (0.0 - 5.0 percent):
FL (LeMieux)
Murray (WA)
WV (Byrd)
Feingold (WI)

Weak Republican, 4 Seats (0.0 - 5.0 percent):
DE (Kaufman)
NH (Gregg)
OH (Voinovich)
PA (Spector)

Strong Republican 4 Seats (5.0 - 15 percent):
Bennet (CO)
Grassley (IA)
MO (Bond)
Burr (NC)

Safe Republican 15 Seats (15.0 percent+):
Shelby (AL)
McCain (AZ)
Lincoln (AR)
Crapo (ID)
IN (Bayh)
Isakson (GA)
Murkowski (AK)
KS (Brownback)
KY (Bunning)
Vitter (LA)
ND (Dorgan)
Coburn (OK)
DeMint (SC)
Thune (SD)
UT (Bennett)

Polling Remains Steady, Republicans Expected to Gain 43 Seats

Based on polling data released over the six 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 43 seat gain by Republicans, down slightly from the previous estimate. This result is almost identical to the previous month's estimate. However, one should note that polling has been sparse for the last several weeks. If the polling holds steady, Republicans seem to be poised to retake control of the U.S. House of Representatives.

A statistical model that analyzes the results of 15 independent polling firms indicates that Republicans lead Democrats by a margin of 1.4 percent on the so-called generic ballot--a measure of national voter preference between the two major congressional caucuses. This figure is slightly greater than the May estimate of 1.3 percent. The June estimate implies that, if the election were held today, Republicans would achieve a bout a 11 seat majority over Democrats--a very modest advantage.

Over the next five 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.