Internet polls are regularly underestimating support for Hillary Clinton

Since the Republican and Democratic conventions in July, Hillary Clinton has experienced a poll ‘bounce’, to lead Donald Trump by about 8 percent, especially in telephone polls with live interviewers. Internet polls, by contrast, tend to show Clinton leading by only 2 or 3 percent. Are these internet polls underestimating Clinton or overestimating Trump? Using results from the 2016 presidential primaries to assess state polls’ accuracy, Taylor Howell, Christopher Stout and Reuben Kline find that that internet polls were slightly more likely to overestimate support for Trump than live interviewer polls, and that they were likely to underestimate support for Clinton by nearly 2 percent. They suggest that online polls may still have some ways to come in terms of accuracy and may be skewing away from Clinton by offering a “don’t know” option to those who are as yet unwilling to commit to voting for her.