Polling Misses Mark in Oregon Presidential Primary

A major public opinion poll conducted before the Oregon primary showed Hillary Clinton outpacing Bernie Sanders by double digits. Actual election results were almost the exact opposite.

A major public opinion poll conducted before the Oregon primary showed Hillary Clinton outpacing Bernie Sanders by double digits. Actual election results were almost the exact opposite.

A well publicized public opinion poll conducted between May 6 and 9 showed Democratic frontrunner Hillary Clinton leading challenger Bernie Sanders in the Oregon primary by a 48 to 33 percent margin. Actual election results were almost the opposite, with Sanders carving out a double-digit victory.

How could a poll be so out of whack? One frequent reason is failure to account for voter turnout. However, the Clinton-Sanders poll took higher-than-average turnout into account, which showed Clinton’s lead narrowing to 45 to 38 percent. Still wrong, by a wide margin.

The same poll, which interviewed 901 likely Oregon voters, under-predicted Donald Trump’s vote count. He received 45 percent of the GOP presidential vote in the poll, but almost 65 percent of the actual vote. Another big miss.

Telephone surveys have become somewhat less reliable if they don’t include a percentage of cell phone users, which ensures that younger and minority voices are heard. While that sampling flaw might understate the vote in Portland or college towns like Eugene, it doesn’t explain Sanders’ strong showing in rural Wallowa and Lake counties or his dominance in all but one of Oregon’s 36 counties.

Candidates usually do better in states where they campaign in person. Sanders appeared in Oregon four times before the primary. Clinton made no appearances, but did send Bill Clinton to campaign. That’s a hard factor to capture in a public opinion poll, but it is a question worth asking to see if being here breaks someone’s vote one way or another. 

The Los Angeles Times carried a story over the weekend about the intense Democratic push in Oregon to register new voters as Democrats before the April 26 deadline. Many of the new voters were automatically registered as a result of Oregon’s Motor Voter law, but not affiliated with any political party. Secretary of State Jeanne Atkins reported a larger than normal registration switch, which favored Democrats. These factors would have been hard to track in a poll, but they may have been worth asking about to gauge the velocity of a late shift toward Sanders, who predicted he would win if the turnout was large. He obviously knew what he was talking about. 

Polling is a tough business, and it is getting tougher. Fewer people are willing to be interviewed by phone, which means pollsters need to make more calls to achieve a representative sample, which is more costly. Respondent reticence means polls have to take less time and include fewer questions, sometimes the questions that would be useful in improving confidence in poll findings.

While Sanders’ success in Oregon is not a huge surprise, it may be more telling than at first glance. His victory points out the foibles of one-off polls and the political benefits of an intensive ground game. 

More significantly, the results in Oregon show Sanders’ message packs some punch, and not just where you would expect.