How mail-in ballots might confuse polls - and Election Day results

Election Day is more than two weeks off, and anything can happen in many key races that could determine the shape of the next Congress.

But millions of Americans already are able to vote, and many of them have marked their ballots as Election Day turns into “election month” across much of the country. More and more states are making it easier to file absentee ballots, and many states are allowing mail-in ballots to be postmarked (not just received) on Election Day.

This prolongs ballot counting, which means that in close races it could be days after voting stops before some races are decided. The practice can also throw off pre-election polls – those closely-watched indicators used to shape last-minute campaigning.

Take the US Senate race in Washington State, where three-term incumbent Democrat Patty Murray is in the fight of her life against Republican Dino Rossi.

Since 1993, voters there have been able to vote by mail, and ballots are mailed out at least 18 days before the tally begins. King County, which includes Seattle, switched to all-mail voting last year.

As polling expert Nate Silver of FiveThirtyEight.com points out, “This can wreak havoc with traditional likely voter models.” (The trend among younger voters to eschew landlines in favor of cell phones, making it harder for pollsters to find them, also throws off polling, he says.)

Voting from home increases turnout

Making it easier to vote by mail – not requiring a reason when a request for an absentee ballot is made – also has tended to increase turnout, Mr. Silver points out, and this can skew traditional polling and voting patterns. In the last midterm election in Washington State (2006), 88 percent of voters mailed in their ballots.

The situation is similar in Oregon, where all voting has been done by mail – there are no polling places – since voters approved a referendum in 1998. But this is not just a Pacific Northwest phenomenon.

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