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 pre-determined or exogenous variables: (1) the number of House seats won by the in-party at the previous midterm election, which registers the impact of institutional advantages enjoyed by incumbents in the US single-member district, constituency service-oriented legislative system, and (2) weighted-average growth of per capita real disposable personal income over the congressional term. No other objectively measured, persistent factor systematically affects on-year 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_t-8 is the number won by the president’s party at the previous midterm election eight quarters ago, and ΔlnR is the quarter-on-quarter log-percentage 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 1952-2008 yields the following coefficient values and related statistics

Coefficient estimate:					Adj. R^2= .89
(Std. error|p-value):	(20.4|.82)	(0.09|.00)	(1.8|.00)	(0.2|.00)	Root MSE = 13

The Democrats won 193 seats in the 2010 House mid-term election, a loss of 63 from their 2008 on-year 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 -- weighted-average 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 weighted-average 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 mid-term 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 on-year elections 1952-2008 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 13-15%, 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 political-economic 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 pre-election poll readings of voter sentiments, preferences and opinions. Trends and related time-coded variables are ad-hoc, statistical junk without scientific merit no matter how much they improve statistical fits or forecasting accuracy in various samples. Attitudinal-opinion 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 mid-term House elections based on my Bread, Incumbency and Balance model.