CBS News' 2010 National House Model: What Does the National House Vote Mean?

Before an election, the "generic" national House preference is often used to indicate how the battle for Congress is going. We see this reported in national polls all the time.

But the House isn't decided by a national vote, of course - it's 435 separate elections - and that generic vote number leaves us wondering what it specifically means for seats won or lost. So how can we translate the national House vote into prospects for House control?

This CBS News 2010 National House Model offers some guidance.

It is a mathematical simulation of how possible national vote outcomes could affect all 435 seats -- based on a CBS News Election team analysis of historical voting patterns, the past and present characteristics of 435 districts, and the current competitiveness level of all districts in 2010.

Note that this is not a poll.... nor is it a prediction; it's a guide to understanding what the national numbers you see might really mean in today's context. Importantly, this is a national model that cannot say which individual districts will flip or not - and it isn't designed to do that. It's about how many. Nor are we predicting any outcomes for a party at this point. We'll have to wait for election night for that, when the real votes are counted.

A complete description follows, but first, the results:

• As of today, a national two-party vote of 52 percent or more Republican indicates the GOP would probably win enough seats to take control of the House on Election Day.
• But in this environment with so many competitive and tossup districts, very small changes in national vote are equated with meaningful shifts in the possibilities for House control.

With 52 percent of the two-party national vote, the model shows that Republicans could end up with 226 seats (they need 218 for a majority) and most likely get something in the range of 215 and 237 seats.

Think of that range as a bit like a margin of error -- and yes, it is a wide range, but that's a reflection of the large number of tossups still out there, which the model necessarily takes into account. If Republicans get that 52 percent, the number of Democratic seats would drop into a range between 198 and 220 seats, with the most likely specific outcome being 209 seats, and loss of control.

• A 51 percent national vote would mean House control is a razor-close tossup. If you see that in the polls right before Election Day, expect a tight race for control as the votes are counted. Republicans still make gains, and would expect to draw about even with the Democrats at around 218, but the ranges of the estimate are wide enough that either party could end up with narrow control in that kind of a tight national vote scenario.
• If Democrats keep the national two-party vote even, that would be a sign that they could keep control, though the GOP would pick up seats. In a dead-even national vote scenario, the Republicans would make gains and eat away at the Democrats' sizeable current majority, but get to 210 seats while the Democrats would retain 225.

How the Model Works

Movement in the national vote is often described as a wave that picks up more and more districts in its wake the bigger and bigger it gets. That's not a bad metaphor - but we need to translate it into numbers.

First, we start with what we know about the national house vote: it is really made up of the aggregate Democratic and Republican totals from 435 distinct contests. We also know that individual districts won't all move perfectly in concert with the national vote in a Democratic or Republican direction; some will be more sensitive than others to any national movements we see.

Critical Contests: CBS News Election 2010 Race Ratings

See all Ratings for Senate, House and Governors in an Interactive Map (Updated Oct. 18)

You can picture this if you consider that some districts will inevitably have more independents or swing voters than others. Or that local contests will insulate many districts from national trends: for instance, think of all the House districts (and there are many) where long-time incumbents reliably collect the same percent of the vote every year and are on pace to do so again. Now think about those compared to districts where there are wide-open races with voters vacillating between candidates. You'd imagine the latter type could be responsible for relatively more of the total national movement that we see.

So with that in mind, we build a model that takes into account a variety of characteristics in each and every House district that could (and do) impact the Democratic and Republican vote shares, including whether it is an open or incumbent-held seat; its past vote history in this decade; the level of competition it saw in all of those years; what kind of national election (midterm or presidential) it was; demographic data for the district; the increases or decreases in turnout year to year, among other factors.

To understand how sensitive every type of district is to the national vote, we analyzed exactly how those types of districts varied in their own district-level vote compared to the aggregate national vote every year. In doing that comparison, we controlled for each of those district-level characteristics, so that we could isolate their impact.

Next, though, we have to remember that it's not just about movement in vote - it's ultimately about winners and losers in every district. A party falls over the 50 percent line and wins, or under, and loses. So we need to know whether variations in vote will make a district flip parties, and that depends not just on size of the movement but on how close each of the contests is in every district. A district whose voting routinely hovers around 50 percent for each party doesn't take much of swing to tilt it one way or the other; it only takes a little swing to flip a 51-49 Democratic district, for instance, to a 51-49 Republican win. But in a district, say, where a Democrat routinely wins around 70 percent of the vote, even a big 10 percent swing toward the GOP won't matter in who wins and loses; the Democrat would still win with 60 percent.

So when we know the degree to which vote changes in any particular district (based on all it's characteristics) is associated with changes in the national vote, and we know how closely contested the partisan divide is in all the districts, we can put the two together and simulate how many would "flip" parties as the national vote share - the assemblage of all those districts results - swings to and fro.

For 2010, in addition to the past profiles, we know and include in the simulation the level of competitiveness of all 435 districts in 2010 from the CBS News Critical Contests lists, some of which are edging Republican, some edging Democrat, and some are pure tossups.

This is about understanding how swings in the national vote could affect the number of seats that turnover and swing control of Congress, and is, hopefully, a useful guide to interpreting what all that movement in the national generic numbers could ultimately mean. When you see a national generic used as an indicator of the House, you'll know, with a little more specificity, what it indicates.

As more individual districts change in their ratings of competitiveness, we'll update the model again.

Analysis by Anthony Salvanto and Tiffany Washburn.

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Anthony Salvanto is CBS News Elections Director. You can read more of his posts in Hotsheet here.

[Renewable216]

Question for President Obama on October 25,2010

Why did the Nantucket Wind project pick New Bedford over Quonset Point, Rhode Island

The City of New Bedford, Massachusetts or state doesn't even own the land for the proposed Nantucket Wind project! ? They have to buy it or take it by eminent domain!
?
The New Bedford site selection is yet another case where there are now more questions than answers, many of them as simple as who owns the property and why it needs to be taken by eminent domain. Announcing tens of millions of taxpayer dollars for a site the state does not yet own is nothing more than an election season stunt. New Bedford officials are still in talks with private landowners who control portions of the property!

The New Bedford site selection is further evidence that the Nantucket Wind project is rapidly evolving into another Big Dig - a money pit with no end in sight to taxpayer bailouts. The development and rehabilitation of the New Bedford site would cost taxpayers upwards of $35 million. If the project is built, Cape Wind developers are asking for another estimated $600 million in federal stimulus money. All this for a project that would pay only $88,000 in annual lease payments.

Quonset Point is an old air force-navy base ready to go! Every Rhode Islander should be asking why Massachusetts is about to spend 635 million dollars of stimulus funds to build
a wind turbine site when Quonset Point was built 40 years ago!

[nearl451]

Don't think Obama blogs this site. You may have to try a difrent forum.

[stn_sage]

It's very unfortunate that the public has to suffer the likes of either Pelosi or Boehner as Speaker of the House! Neither is worth a ...!

[Mortarman329]

True.

[Amusedbyitall]

Truly, this article gives an indication of gridlock for 2011-2012.

[Mortarman329]

Which is EXACTLY what we need. Shut the place down!!

[doctor_know]

You actually want to cripple the government? That's moronic....

[infantryman1968]

CBS News' 2010 National House Model: What Does the National House Vote Mean?
LOL! It means Nancy is fired and Obama will be fired in 2012!

[Cattzen]

Dennie Hastert, Tom Delay, Mark Foley and a complete HOUSE OF CORRUPTION was the reason the Democratic Party retained the Majority.

The Democratic House (with Republicans) composed the HealthCare Bill most Americans would have been more satified with and, still should be reviewed for improving the current Healthcare Reform Act that was completely polluted by the Republicans in the US Senate.

A vote for the GOP is another vote against Americans.

[JWinATL]

Have you been asleep the last two years? The Republicans had NO say to speak of in the Health Care Bill. They incorporated a tiny fraction of the Republican ideas. The pollution was totally from the Democrats and Obama! Go do some research!

[Mortarman329]

Facts elude Cattzen.

[chatmandu7451]

There is change a comin.... :o)

[Cattzen]

if the GOP gains the Majority then we can all expect more of the SAME detrimental Conservative Corrupt Agenda that crashed the American way of life.


facts.

[strikerF2]

Best thing could happen would be for a change every 4 years from one party to the next. It was during the 40 year Democratic rule they decided to dip into the Social Security trust fund,now look how screwed up it is.

[stn_sage]

Congress was turned over to the Dems because the Republicans did such a lousy job before them! Republican leaders say if they're put back in charge, that essentially, they'll continue to dismantle govt to favor corporations, while the lives of the 'common man' will continue to erode!

But, if the Dems somehow 'hang onto' Congress, do they plan to begin to fulfill Obama's pre-election agenda? Or, are they going to continue to work for corporate America against the public? Neither party appears to care at all for the body that gave them THEIR jobs, that is, the public!

The situation appears to be; if you want quick destruction, vote GOP; if you want slow destruction, vote Democrat! If you want real change, you better try to rally around an "outsider" who doesn't belong to either of the 'Big Two' parties!

[Cattzen]

It would defy logic that Americans dissatisfied with the conduct in Washington would return majority rule back into the hands of the one's that fostered the recession, wars, increased spending, and rampant corruption.


The Republicans in Congress have done ABSOLUTELY NOTHING in regards to economic recovery, restoration of jobs, and increasing the life standard of living to the American Working Middle Class.


The GOP by their actions of denying everything that would benefit Americans is the Party of "NO!" And, simply do not deserve a vote to command a majority rule in either house of congress.

[strikerF2]

From 2006 to 2008 when the Democrats rulled the house what two bills were passed? 2 bills in two years what are we paying them for. One was Cowboy Day Recognition,and one was the minimum wage bill. Then they put no strings on tarp,or the stimulis,just spend,spend,spend.

[Cattzen]

Why are we paying the Republicans for just road blocking, impeding, and saying "NO!"????


The GOP does not deserve the Majority because they have done nothing for the American People.

[tsigili]

That would indicate that if Dems outnumber the GOP, they win by default, on sheer numbers, and that is DANGEROUS for this country.

[briefer]

If you think that one group of voters outnumbering another group of voters is "dangerous" then you need to have a little chat with the Founding Fathers. Your complaint is with them. I think that's called Democracy.