But it’s impossible to know which party will benefit. Silver explains:
In a number of elections, including 2012’s, Senate polls had a systematic bias toward one party. But the direction of the bias has been inconsistent, favoring Democrats in some years and Republicans in others. The chart here depicts the average partisan bias in Senate polls of likely voters conducted in the final three weeks of campaigns since 1990. (For raw data from 1998 onward, see here; for 1990 through 1996, see here). A year indicated as having a Republican bias means the GOP underperformed its polls. A year shown as having a Democratic bias means the Democrats underperformed theirs instead.
In 2012, Senate polls had a Republican bias of about 3.5 percentage points. That means in a state where the polling average showed the Republican ahead by a point, the Democrat would be expected to prevail by 2.5 points instead. If there’s the same bias in the polls this year, Democrats would be very likely to keep the Senate.
But as I mentioned, this bias has flipped back and forth.
Waldman rejects the notion that Democrats are unskewing polls this election cycle:
What Democrats are doing is arguing that whatever the polls now say, they’ve got a great turnout operation this year, and that’ll make a big difference come election day. Or they’re expressing the hope that in a couple of key races, voters will eventually wise up and understand the radicalism of the Republican candidate. But that’s very different from arguing that the polls are systematically skewed against them. One is about expressing optimism and keeping your side motivated, while the other is a delusional denial of reality.
The NYT’s model now gives the GOP a 73 percent chance of taking the Senate. Leonhardt puts this percentage in context by listing situations that occur “between 25 and 30 percent of the time”:
■ The odds of rolling a 9, 10, 11 or 12 with two dice
■ The chances that a blackjack casino dealer busts
■ The percentage of calendar years since World War II that the Standard & Poor’s 500 has declined
■ The share of days in which it rains in Kansas City (as it did Monday, postponing a baseball playoff game)
■ The frequency with which a 25-year-old woman is shorter than 5 feet 3 inches
■ The frequency with which a 25-year-old man is 5-11 or taller
■ The odds that a National Football League defense prevents a first down on third-and-one.
He insists that, if the GOP’s odds stay roughly the same through election day, “it won’t be right if the Republicans win any more than it will be wrong if the Democrats keep control. “
The Dish 