45 Years Of House Ballot Polling Finds Pollsters Typically Overstate Democrats Actual Performance

Image on the left is courtesy of Alaskans For Begich TV ad, and highlights the wealthy, mega-donors Koch Brothers support of Republican candidates. Image on the right comes from an anti-Obamacare ad sponsored by Generation Opportunity.

Glancing at the current HuffPollster and RCP polling averages, Democrats and Republicans are essentially tied on the generic House ballot question. The former finds Republicans ahead by less than half-a-percentage point, while the latter finds them down by a roughly equal margin. But don't expect the same polling dynamic that exits today to be present on election day - at least not if past generic House ballot polling dating back to 1970 has anything to do with it. And further, I'd caution against relying too much on the surveys taken in the final week before the election, too, as they've been pretty hit-or-miss themselves.

Hundreds of generic ballot surveys taken over the last 45 years and eleven midterms finds polls conducted in the Spring of an election year (April, May, and June) have overstated the eventual Democratic margin in nine of them, or 82% of the time (including the last five midterms in a row). Surveys taken in the final week(s) of a campaign are no exception, understating the Republican margin in eight of eleven elections. Consider the tables below, the first of which provides polling data in the spring of each midterm since 1970 compared to the final result, the second of which compares polling data taken in the final week(s) of the campaign with the actual result.

Polling data pre-2006 was provided by the Roper Center's IPOLL databank. * Indicates the cutoff date for polls to be included in the average was TWO weeks prior to the actual election day. ** Indicates the cutoff date for polls to be included in the average was THREE weeks prior to the actual election day. Dates were only altered if necessary to obtain a large enough sample to average.

Surveys conducted in the Spring of the last eleven midterm elections tended to overstate the eventual Democratic margin over Republicans by an average of five net points. Looking at specific elections, such as 2010, you can see Republicans were polling an average 43% in the Spring of that year, though they eventually won 51% of the popular vote. Democrats, meanwhile, were polling an average of 42% that Spring, and wound up with 45% that November. The Republican advantage over Democrats grew from just one point in April, May, and June, to six points in November.

Lessons from 2010, 2006, & 2002: Why You Shouldn't Read Too Much Into Early Generic Ballot Polling

Democrats are polling slightly ahead of Republicans in the generic ballot. But the GOP is still better positioned than at this point in 2009.

It's been a rough few months for President Obama, both in terms of polling and external political events.

Barely 6 months into his 2nd term, he's seen both his job approval and favorability ratings slide, while unexpected and distracting scandals involving the IRS and the NSA have angered both opponents and allies.

Yet for all the President's troubles, his party has held up well, at least from the perspective of 2014 Midterm Election polling to date.

Excluding Rasmussen Reports, the Republicans have led the Democrats in only one generic House ballot survey taken since the November 2012 election (out of 26 total polls), and have averaged a 43-40% deficit against the party that currently holds the White House and the Senate. See the table below:

*because Rasmussen tracks the generic congressional ballot every week, their numbers in the above chart are monthly averages. Data compiled from Huffington Post Pollster, Real Clear Politics, & TPM Polltracker.

The Democrats' 3 point house ballot advantage seems all the more impressive when considering the fact that the President's party very rarely performs well in second-term, midterm elections.

But try not to draw too many conclusions from the current state of polling regarding the 2014 election, especially considering the state of generic House ballot polling at this point in 2009.

From immediately following the 2008 Presidential election, until August of 2009, the Democrats averaged a House ballot lead over the Republicans of 44-38%; this, at the beginning of an election cycle in which the Republicans ultimately won the national House vote by 51-45%, and gained 63 seats in the House of Representatives.

Rasmussen & YouGov/PoliMetrix tracked the House ballot weekly. Their numbers in the chart above represent monthly averages. Data compiled from Huffington Post Pollster, Real Clear Politics, and Polling Report.

In other words, Republicans performed a net 12 points better than the average of polling at this point in 2009 predicted. Furthermore, at this point in 2009, Republicans led Democrats in only 4 of the 38 generic ballot polls taken since the November 2008 election, as compared to leading in all but 2 of the 39 surveys conducted in the final month of the 2010 election.