Oh, Mitt, first The Senate, now The House?

[mshan]

Then (the Ryan pick):

"My takeaway: Romney effectively threw Congress under the bus to get a possible (but not guaranteed) advantage for himself. Call it a calculated risk on his part."


http://election.princeton.edu/2012/08/15/ryan-is-a-game-changer-but-not-for-romney/

Now (the 47% comment):

"First, to quote Matthews’s claim:

John Sides and the team at the Monkey Cage have a model that uses GDP, the president’s party and approval rating, incumbency, and district-level presidential vote, rather than House polling. Their model gets the seat margin wrong by 2.61 seats, on average, much lower than Wang’s error. It gives Republicans a three out of four chance of keeping the House.

This is seemingly a convincing criticism. However, at its heart is some misdirection. The “2.61 seats” statement is revealing because it is too small to be realistic. It is the same weakness I detected in the FiveThirtyEight “four-factor” model yesterday: Overfitting of small residuals is basically chasing noise, and leads to massive uncertainties.

Now, the Monkey Cage crew is aware of this issue. To quote them:

The standard error for the vote share estimate is 5.6%; for seat share, 8.7%. That’s a lot of uncertainty. It means there is at least a little probability of some pretty crazy outcomes. It explains why there is still a 1 in 4 chance that the Democrats will get the 25 seats they need to retake the House, when our own median prediction is only one seat.

In other words, the “median gain of one seat” sounds precise…but is meaningless.

Let me make the point graphically. Here are our two national-popular-vote predictions plotted side by side…but with uncertainties included:

For those of you unfamiliar with this kind of plot, the data points are the values that get reported in the popular press. The horizontal lines are error bars. They indicate the confidence with which we know the median. A large error bar indicates high uncertainty.

As you can see, our two ranges are perfectly consistent – but the PEC estimate gives much more certainty – and information. In contrast, their range, from R+13% to D+9%, contains many possibilities that we can be confident will not happen in November. If the Republicans win by 10 points, I will personally wash Dylan Matthews’s car with a toothbrush.

What about seat count, the ultimate measure of House control? Same story:

In short, their model indicates a three in four chance of GOP control because their uncertainty is massive. Do you think the Republicans will attain a 278-157 majority?

In some sense, our two calculations are consistent. However, what I presented is not a complex model in the same sense, but a precise short-term projection of likely outcomes.


http://election.princeton.edu/2012/09/21/monkeying-around-with-fundamentals-based-models/#more-5986

Mitt, Mitt, Mitt...

 

[mshan]

"The trend in the presidential race has been difficult to discern lately. President Obama has very probably gained ground since the conventions, but it’s hard to say exactly how much, and how quickly his bounce is eroding.

There are no such ambiguities in the race for control of the Senate, however. Polls show key races shifting decisively toward the Democrats, with the Republican position deteriorating almost by the day.

Since we published our initial Senate forecast on Tuesday, Republicans have seen an additional decline in their standing in two major races.

Two polls of Virginia published on Wednesday gave the Democrat, the former Gov. Tim Kaine, leads of 4 and 7 percentage points over the Republican, the former Senator George Allen. The FiveThirtyEight forecast model now gives Mr. Kaine roughly a 75 percent chance of winning the seat on the strength of the new polls, up from about 60 percent in Tuesday’s forecast.

The other problematic state for Republicans is Wisconsin, where their candidate, the former Gov. Tommy Thompson, had once appeared to hold the advantage.

Mr. Thompson’s Democratic opponent, Representative Tammy Baldwin, had published an internal poll earlier this week showing her pulling into the lead.

The FiveThirtyEight Senate and presidential forecasts do not use internal polls released directly by the campaigns, as they typically exaggerate their candidate’s standing."


...


"Some of these theories are speculative, to be sure. A large number of Senate races remain in play: of the several states in which there has been a shift against Republicans in the polls in recent weeks, perhaps only Florida seems completely lost.

But if the trend continues, the question may no longer be whether Republicans can win the Senate — but how vulnerable they are to losing the House."

http://fivethirtyeight.blogs.nytime...ast-what-has-gone-wrong-for-g-o-p-candidates/