It looks like this absurd and lurid presidential election will remain unpredictable until the end. Between the FBI’s on-again, off-again investigations of Democratic candidate Hillary Clinton’s emails, the “you can do anything” comments from Republican rival Donald Trump—not to mention the unexpected injection of Anthony Weiner’s ongoing sexting habits—it’s hardly surprising that the polls seem to show wild swings in voter views.
Our experience as pollsters, though, shows this isn’t so. It’s true that daily tracking surveys reflect dizzying twists and turns in support for Trump and Clinton. If you compare the single daily tracking poll from our own Reuters/Ipsos with the Huffington Post/Pollster poll aggregator, you’ll see what looks like lots of movement in support for both candidates. Over five days the number of Trump backers rises from a little over 30 percent to around 40 percent; Clinton’s support fluctuates between 40 percent to almost 50.
However, these momentary swings disappear when we look at monthly averages instead. The larger slices of time show that the rapid swings in voters’ views always return to a rough equilibrium. In fact, there has not been any real change in Trump and Clinton’s relative position over the last three months. In July, Clinton had a 4 percentage point lead over Trump and in October, she still has a 4 percentage point lead. The most recent polls show that this lead may have narrowed since FBI director John Comey announced last Friday that he was re-opening an inquiry into Clinton’s emails, but our experience suggest that this number may also revert.
Why has support for candidates Hillary Clinton and Donald Trump been so stable?
The reason is that most Americans already know –and have known for awhile—who they support.
Despite this election being characterized by “swing-ier voters,” this race has pretty much been on cruise control for most voters.
At the start of this year, an overwhelming 99 percent of Americans had heard of Clinton and 98 percent had heard of Trump. Only 24 percent of Americans had neutral opinions of the Democratic candidate and 23 percent of the Republican. Voters have been exposed to Clinton and Trump in one form or another for more than 30 years; they knew what they thought of them.
What the daily polls are actually showing is the waxing and waning of enthusiasm among existing supporters of the presidential candidates. They’re doing this in two ways. First, through use of “likely voter” filters. Most likely voter filters, including our Reuters/Ipsos one, include a measure of voter enthusiasm (along with things like registration and past behavior) as part of determining whether the respondent will turn out to vote. As the enthusiasm of respondents increases or decreases, they are more or less likely to be classified as a likely voter and therefore reported in our ‘horserace’ polling. When events excite or depress the base, these show in our polling. Our five-day rolling average of enthusiasm to vote among Clinton and Trump supporters since July shows shifts in likely turnout tend to correlate with shifts in the polls.
The second way polls are showing shifts in enthusiasm is (potentially) through something called “non-response bias.” Non-response bias is the idea that groups of people may be so discouraged by the events of the campaign that they do not even answer surveys when they are contacted. We say potentially because this is hard to measure directly — we cannot survey the people unwilling to be surveyed — but research has shown that this could have a significant impact on temporary poll shifts (link). However, we can see some of this impact by observing the stated party preference of our poll respondents over time.
The Reuters/Ipsos poll does not normally sample, quota, or weight the partisan identification of our respondents. Since party identification is subjective– a personal stated allegiance rather than an objective demographic — there are no commonly accepted benchmarks for the “right” party composition of the electorate. That means we ask people how they identify and they answer as they answer. However, the partisan composition of our poll — and most other polls — can fluctuate substantially over time. Since July, the Reuters/Ipsos polls show that as these scandals occur, people with strong party affiliation are less likely to respond to a poll.
This is far from a ‘flat’ line and it underlines the extent to which these identities are variable based on political dynamics and events.
Chris Jackson is a vice president at Ipsos and runs the Reuters/Ipsos poll. Alanna Spurlock is a research analyst at Ipsos.