The onslaught of presidential polls has already begun. You may be tempted to avoid the polling deluge, but the results of these surveys do influence the campaign, including who will get invited to the first G.O.P. debate. That’s why we want to show you how to read (or ignore) the polls like a pro.
Polls with surprising or novel results can be irresistible to journalists and the public alike. It’s newsworthy if public attitudes seem to have changed in some unexpected way. As a result, these findings tend to attract the most public attention and media coverage. Unfortunately, they are the most likely to be spurious.
What looks like a shift in public opinion is often just random statistical variation. First, all polls should come with an associated margin of error or some other estimate of uncertainty. Take it seriously. With the sample sizes conventionally used in polling, changes in support of one or two percentage points can’t be distinguished from random variation. Second, given the number of polls that are conducted, outliers are likely to be common. Approximately one in 20 polls of President Obama’s approval rating, for instance, will produce a statistically significant change from the last estimate even if nothing changed.