How to Be Misled by Polls, Hillary Clinton Email Edition

Has the controversy over Hillary Clinton's use of a personal email account hurt her in the polls?

You might think so if you read a CNN article published Monday night, which reported that "unfavorable views of Hillary Clinton are on the rise" after disclosure of her use of the email account while serving as secretary of state. (The network's televised coverage of the poll made similar claims.)

This framing suggests that her standing with the public has declined considerably. In fact, the new poll actually seems to be good news for Clinton, the presumptive Democratic presidential front-runner. CNN found that 53 per cent of Americans have a favorable view of her, which is somewhat higher than in other recent polls, including those conducted before the controversy.

CNN's poll seemed to suggest a decline because the network ignored numerous polls conducted by other organizations in the intervening months and instead compared her current standing only with its most recent poll - an outlier from November showing Clinton with a 59 per cent favorable rating.

This approach is misleading for two reasons. First, CNN gives its own poll too much weight compared with polling averages, creating a perception of decline in Clinton's ratings that could be a result of sampling error. (Polling averages are generally more accurate than any individual poll.)

It's even more problematic, however, to compare polls from November and March and attribute any changes that took place over a four-month period to the email controversy. In reality, this comparison cannot distinguish between the effects of the email controversy and the continuing decline in Clinton's favorability ratings as she transitions back into what she was before her stint as secretary of state: an intensely polarizing political figure. (Similar problems plague a comparison by McClatchy of Clinton's standing in trial heats against possible Republican general election opponents with a previous poll in December.)

A broader look at Clinton's ratings suggests, as expected, her standing has so far changed little even as views of the controversy have quickly polarized. As a matter of pure politics, this controversy is most important not for what it tells us about her position with the public at large but with two other constituencies: Democratic Party elites, who remain overwhelmingly supportive, and members of the news media, who appear likely to continue their antagonistic relationship with Clinton.