Douglas Hibbs
July 27 2012
The Partisan Division of House
Seats in 2012: Implications of the ‘Bread and Incumbency’ Model
for Democratic Party Prospects as of
2012:q2
The number of House seats won by the president’s party in presidential
election years, whether it be in the majority or the minority, is well
explained by just two fundamental predetermined or exogenous variables: (1)
the number of House seats won by the inparty at the previous midterm election,
which registers the impact of institutional advantages enjoyed by incumbents in
the US singlemember district, constituency serviceoriented legislative
system, and (2) weightedaverage growth of per capita real disposable personal
income over the congressional term. No other objectively measured, persistent
factor systematically affects onyear House election outcomes.
Unlike votes for president, US military Fatalities owing to unprovoked hostile deployments of American
armed forces in foreign conflicts exert no systematic influence on the aggregate
partisan division of House seats. In present circumstances, political
responsibility for American Fatalities
in Afghanistan will be attributed to President Obama, not congress.
The Bread and Incumbency equation for the
partisan division of House seats is written
where Seats_{t} denotes the
number of House seats won by the president’s party at presidential election
periods, Seats_{t8} is the
number won by the president’s party at the previous midterm election eight
quarters ago, and ΔlnR
is the quarteronquarter logpercentage rate of growth of per capita real
disposable personal income expressed at annual rates, computed where R
is per capita disposable personal income deflated by the Consumer Price Index.
Estimating
the Bread and Incumbency equation for
the fifteen House elections in presidential election years spanning 19522008
yields the following coefficient values and related statistics
Coefficient estimate: 




Adj. R^{2 }= .89^{} 
(Std. errorpvalue): 
(20.4.82) 
(0.09.00) 
(1.8.00) 
(0.2.00) 
Root MSE = 13 
The
Democrats won 193 seats in the 2010 House midterm election, a loss of 63 from
their 2008 onyear showing of 256 seats, which put the president's party in the
minority for the 112th Congress. Over the first 6 quarters of the 112th
Congress  2011:q1 to 2012:q2  weightedaverage growth of per capita real
income was an anemic 0.57% according to the latest revision of the National
Income and Product Accounts available at this writing posted by the Bureau of
Economic Analysis on July 27 2012. My best guess is that quarterly, annualized
per capita real income growth will fall in the interval [1,2%] during the last
full quarter of President Obama’s term, 2012:q3, which under the Bread and Incumbency model would yield 186
seats going to the Democrats in the 2012 House election. The data in the table
below imply that the prospect of the Democrats winning a bare majority of 218
House seats in 2012 is nil, even under the hugely unlikely event that per
capita real income growth were more than three times the upper limit of +6%
shown in the last column of table.

Expected
Number of House Seats Going to the Democrats in 2012 at various real income growth rates 2012:q3 

Hypothetical
per capita real income growth rate 2012:q3: 
4 
2 
0 
+1 
+2 
+4 +6 

=>
Resulting weightedaverage real income growth rate over the congressional
term: 
0.6 
0.1 
0.4 
0.7 
0.9 
1.5 2.0 

=>
Expected number of seats going to the Democrats – the president’s
party: (Change
from 2010 midterm election result of 193 Democrat seats) 
177 (16) 
180 (13) 
184 (9) 
185 (8) 
187 (6) 
190 194 (3) (+1) 

The Bread and Incumbency model prediction of
186 seats for
the Democrats in 2012 along with actual and fitted values of seats won by the
president’s party at postwar onyear elections 19522008 are graphed in the
figure below.
Like
my Bread
and Peace model of votes for president, the Bread and Incumbency model paints a bleaker picture of the Democratic
Party’s chances for a House majority in 2012 than current betting price data
do. At the end of February 2012 both Intrade
and Iowa
Electronic Markets trading prices implied that the chances of the Democrats
winning a House majority in 2012 was between 1315%, down from 35% in February
2012.
Both the Bread and Peace model
and the Bread and Incumbency model
aim to explain election outcomes in
terms of objectively measured politicaleconomic fundamentals, rather than to
predict optimally voting results or to track them statistically after the fact.
For those reasons neither model includes arbitrarily coded dummy, trend, or
count variables or uses preelection poll readings of voter sentiments,
preferences and opinions. Trends and related timecoded variables are adhoc,
statistical junk without scientific merit no matter how much they improve
statistical fits or forecasting accuracy in various samples.
Attitudinalopinion poll variables are themselves affected by objective
fundamentals, and consequently they supply no insight into the root causes of
voting behavior, even though they may provide good predictions of election
results.
Here
are the Stata
program (“do”) file and the Stata
data (“dta”) file that generated results on this page.
Here you will find an analysis of the partisan division
of seats in midterm House elections based on my Bread,
Incumbency and Balance model.