Nate Silver demonstrates a series of calculations we can use, election night, to predict how the numbers will go. He's made a model which he'll use to determined Republican wins and losses for specific seats.
... For instance — the New York 19th congressional district, in which we have the Republican Nan Hayworth favored by 3 points — the magic number is 43. That means that if Republicans won this seat — and all other seats in which they were favored by more than 3 points, but none of the seats in which we had them favored by fewer than 3 points — they would finish with a gain of 43 seats on Democrats over all on the night. Another way to look at the magic number is that it’s the number of seats we’d expect Republicans to win nationwide if they won this particular district by exactly 1 vote (and we had no information about what had taken place in any other district).
Occasionally, the magic number will be negative; these are seats that, if the G.O.P. lost them, would imply that it were actually going to lose seats in the House overall.
What you should be looking for is whether Republicans are consistently winning seats with magic numbers in the 60s, 70s, 80s or higher. If so, they could be in for a very big night. Conversely, if Democrats are holding onto seats with magic numbers in the teens, 20s, or 30s, that means they are overperforming their forecasts and could hold the House.
Silver's predictions are, so far, at odds with those of the bettors in the Washington Post. Here's where his calculations landed last night.
... Our forecast [for the House] is unchanged for the third consecutive evening: Republicans won an average of 53 seats in our simulations, although they were knocking on the door of 54. We have Democrats’ chances of holding the House at 16 percent, which is unchanged from Friday.
...Republican chances of taking over the Senate are up a tick to 11 percent Saturday from 10 percent Friday. The reason is a Marist College poll showing Patty Murray just 1 point ahead of Dino Rossi in Washington. That’s not a terrible result for Ms. Murray, obviously — she holds the lead, however nominally so, and Marist’s results are unchanged from its poll 10 days ago. Still, it increases Ms. Rossi’s chances in our forecast from 17 percent to 19 percent; our model is very sensitive to any Washington polling.
...Governors: There is no movement of any real consequence in our forecasts. The closest thing to pass for it is the standing of Tom Foley, the Republican nominee for governor in Connecticut, whose chances improved to 16 percent from 14 percent on the basis of a YouGov poll showing him just 4 points behind Dan Malloy.
