Politics

Frequently asked questions about the Presidential Poll Tracker

Answers to your questions about CBC's U.S. election Poll Tracker.

Answers to questions about how the CBC's Presidential Poll Tracker works

CBC News has launched an interactive feature that tracks the polling for U.S. presidential candidates Hillary Clinton and Donald Trump. (CBC)

Below you'll find answers to some of the most frequently asked questions concerning CBC's Presidential Poll Tracker. You can find the detailed explanation of the Poll Tracker's methodology here.

This FAQ will be updated regularly. Send any questions not answered here to eric.grenier@cbc.ca.

So how does this work?

For all the complete details, you can read the methodology here. But put simply, the Poll Tracker combines polls from different pollsters into an average, weighing them by three different factors: the date of the poll, the poll's sample size, and the track record of the polling firm. This average is then used to determine who is ahead, both nationally and at the state-level. The state-level results are then used to project where things stand in the electoral college, which determines who becomes the president. 

What is the electoral college?

There are 538 electoral college votes in the U.S. presidential election. Each state is worth a certain amount of votes (generally, the bigger the state's population, the more votes it is worth). With the exceptions of Maine and Nebraska, the winner of the popular vote in each state receives all of the electoral college votes in that state. So, for example, if Hillary Clinton receives one more vote than Donald Trump in Florida, she gets all 29 of Florida's electoral college votes. The candidate with at least 270 electoral college votes nationwide wins.

Where do the polls come from?

The polls are sourced from Huffington Post Pollster, which includes all polls that meet a minimum standard of disclosure requirements. You can see a list of all these polls here.

Why is the date of the projection behind by a few days? Aren't you updating daily?

Yes, we are! But the date listed on the Poll Tracker is the final date of polling, rather than the date of the update. (The date of the update can be found at the very top of the interactive.) A poll conducted on a Monday, for example, might not be published until Wednesday or Thursday. But the data in the poll only tells us what voters thought on that Monday. So the Poll Tracker's averages are dated to when the last poll in the model was conducted. Doing this makes it easier to track the impact that campaign events might have on the polls.

Why are the projected electoral college votes the same as a candidate's high or low range?

Sometimes, the high or low range of a candidate will match that candidate's projected electoral college votes. The ranges are based on the electoral college votes of the "lean" states. If a candidate is leading in all of the "lean" states, that candidate's projected electoral college votes will equal their high range. In short, this means that — among the states that are considered toss-ups — the candidate is not estimated to have room for growth (or, conversely, is at his or her floor).

Why don't the projections from a past article match the projections in the Poll Tracker?

When new polls are released, the projection is retroactively updated if those newly published polls were actually conducted before the most recent polls in the projection model. This is to ensure that the polling averages for past dates are accurate for that date.

Why aren't there any numbers for Gary Johnson or Jill Stein?

The projected support levels of "Others" is meant to reflect the combined support levels of third-party candidates like the Libertarians' Gary Johnson and the Greens' Jill Stein, as well as unnamed "other" candidates. As Johnson and, especially, Stein aren't included in every poll, it is more difficult to track their individual support and so the support for all third-party candidates combined is tracked instead.

So the candidate with the most projected electoral college votes will win, right?

Not necessarily! Though that candidate is favoured to win, the model cannot make a projection with 100 per cent certainty. In fact, if the high range of a candidate is more than the 270 electoral college votes needed to win, that means that candidate has a good chance of winning. Only if a candidate's high range is below 270 electoral votes is it considered unlikely that the candidate will win. Nevertheless, there is still a chance that the candidate could pull off an upset — even the "Safe" states are projected with 95 per cent confidence.

In addition, the projection is made assuming an election will be held today. Support levels will change between the date the projection is made and voting day.

ABOUT THE AUTHOR

Éric Grenier

Politics and polls

Éric Grenier is a senior writer and the CBC's polls analyst. He was the founder of ThreeHundredEight.com and has written for The Globe and Mail, Huffington Post Canada, The Hill Times, Le Devoir, and L’actualité.

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