Predicting Washington: polling in a vote-by-mail world

Jeff Alworth

The balance of power in the US Senate may come down to the West Coast. And with Barbara Boxer apparently solidifying her lead over Carly Firorina in California, it may come down to Washington. The good news is that recent polling shows incumbent Patty Murray beginning to edge Dino Rossi. An Elway Research poll (a local firm) put Murray ahead by 15 points among likely voters. That's an outlier, but a CNN/Opinion Research poll also gave her an 8-point lead.

However, as Nate Silver points out, Washington state polls haven't been so accurate over the past decade:

One reason could be that it is one of two states, along with Oregon, where voting takes place almost entirely by mail. This can wreak havoc with traditional likely voter models, which often ask questions like, “Have you voted in the election precinct before?” and “Do you know where people in neighborhood go to vote?” — questions that are nonsensical in the context of an election that takes place by post. Also — probably because of mail balloting — turnout in Washington and Oregon has generally been very high, so targets that might work well in other states could fail there. Finally, since many voters in Washington return their ballots well in advance of Election Day, a pollster surveying the race close to Election Day will encounter another type of voter — those who claim to have voted already — which traditional likely voter models are not well designed to handle.

A lot of this is familiar to Oregonians, but here's an Evergreen State quirk: both Rasmussen and SurveyUSA have given numbers biased toward the GOP by about 4.5 points over the past decade. And Elway, the group that gave Murray the 15-point lead this week has, over the same period, been biased toward the Dems by about 3%.

Fascinatingly, in Oregon, the GOP biases of Rasmussen and SurveyUSA are far smaller (1.5% and .8%), even though the two states are similar in voting method, political orientation, and demographics. So riddle me this pollman: what is it about the two states that differs and makes the Washington results so much harder to predict?

I'm not completely convinced by Silver's explanation:

A few other things about Washington State are worth considering. First, Washington, a technologically savvy state, has a somewhat higher than usual number of cellphone-only adults, which pollsters may not be capturing. It also has a fair number of Asian-American voters, who can sometimes be hard to reach because of language or cultural barriers. These things could make a difference at the margins.

Anyone have a better idea of what's going on here?

By Jeff Alworth Oct. 14, 2010