Parsing the Polls: Is a Democratic Wave Building?

by Chris Cillizza
Washington Post

In a March Parsing the Polls we looked at the edge Democrats held over Republicans on a generic ballot question, which, in essence, asks: "If the congressional election were held today, would you vote for the Democratic candidate in your district or the Republican candidate?"

At the time, we decided that although Democrats' advantage signaled considerable unrest in the country toward the majority party in Washington, it was too early in the cycle to draw any broad conclusions about what the generic ballot numbers meant for the fall.

At the time, the average of the last five national polls testing the generic ballot showed Democrats with a 13.4 percent margin. Fast forward six months and that margin has actually increased. Take a look:

Organization Survey Dates GOP Dem Difference
Newsweek 8/10-11 39% 51% 12%
Fox/Opinion Dynamics 8/8-9 30 % 48 % 18%
AP-Ipsos 8/7-9 37% 55% 18%
Post/ABC 8/3-6 39% 52% 13%
CNN 8/2-3 40% 53% 13%

Add those numbers up and the average Democratic generic edge has grown to 14.8 percent -- with 84 days left before the election.

So is now the time to conclude that a Democratic wave is building that will sweep Republicans out of a House majority in November?

The answer, according to Charlie Cook and Stu Rothenberg, is a guarded yes.

"If you take an average of the last three or four polls, because any one can be an outlier in either direction, you can determine which way the wind is blowing, and whether the wind speed is small, medium, large or extra-large," said Cook. "The last three generics that I have seen have been in the 18 or 19 point range, which is on the high side of extra large. That suggests the probability of large Democratic gains."

(There is more, here.)