Late Polls Miss California's Primary Results

The wide disparity among California polls the final two weeks of the June 7 primary election highlight the multiple difficulties polls are dealing with in general and specifically in the 2016 presidential primary season. In the last two weeks of polling of Hillary Clinton and Bernie Sanders, the range of points spread was 18 to 2 percentage points in favor of Clinton.

The final RealClearPolitics average had Hillary Clinton up 47.7 percent to 45.7 percent to Bernie Sanders, or a 2.0 percentage point spread. The final results were 56 percent for Clinton and 43 percent for Sanders, or a 13 point spread. A major miss that captures some of this season’s polling challenges.

California’s challenges include:

• Several repeat polls using same methodology showed Sanders surging toward the end. In the Field poll, Sanders went from 35 percent in January to 41 percent in early April and 43 percent in the end of May poll. Sanders gained 3 points in the LA Times poll. The last three polls published showed a 2 point difference.
• Several reputable polls claimed the race was 10 points or more apart the last two weeks in favor of Clinton. The LA Times/USC reported 10 points, KABC/SurveyUSA 18 points and Hoover/Golden State poll 13 points (3 weeks).
• Several high-profile final events were likely adding to volatility. On Thursday (June 2), six days before the primary, Clinton gave a well-received and intensely reported speech on Donald Trump’s foreign policy. On the final Monday before the primary, the AP called the delegate race for Clinton.
• Not only was public opinion changing under the onslaught of the final Sanders campaign and the Clinton news, but attempting to model turnout was near impossible. New registrants for the Democratic Party exceeded 500,000 and were mostly younger voters likely to trend toward Sanders, but with no voting history. There were 2 million new registrants total since January and 500,000 were Latino.
• The level of interest in the California Democratic primary was unprecedented. It was 48 years ago in 1968 that Robert Kennedy beat Gene McCarthy in a major slugfest, and there have been a few battles of interest since then, such as Clinton winning in 2008 to lose the nomination. But there is simply no model to use to predict turnout, especially of registered independent voters who can participate in the Democratic Party.