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FiveThirtyEight 2020 Popular Vote Accuracy


FiveThirtyEight is a website that was founded as a poll aggregator and now covers news on a variety of topics with a focus on statistics, polling, economics, and related subjects. It has had notable forecast successes in the past and had among the highest likelihoods for Donald Trump among several forecasters in the 2016 election. It continues to provide polling averages as well as a 2020 election forecast.

Trump's election in 2016 was a surprise to most forecasters, in part due to polling error that showed Hillary Clinton as having a larger level of support than actually materialized in the election. One hypothesized contributor to polling error in the 2020 election is the "shy Trump voter" effect, in which Trump voters do not tell others how they intend to vote for fear of political backlash. The existence of this effect is still under debate; FiveThirtyEight's team discussed this possibility on its Politics podcast and generally considered it unlikely.

How will Trump's popular vote share compare to FiveThirtyEight's prediction?

Trump's predicted vote share (among Biden and Trump votes) will be computed by dividing his popular vote share in FiveThirtyEight's forecast by the total of Trump's and Biden's vote share in that forecast (thus disregarding third party candidates). Trump's actual share of the 2-party popular vote would be calculated in the same way, and the question resolves as the actual 2-party vote share minus the predicted 2-party vote share.

For example, suppose FiveThirtyEight shows 50% Biden and 40% Trump. Then Trump's vote share would be 40/90 = 44.4%. Now suppose the actual popular vote is 40 million Biden, 38 million Trump and 200 million Kanye West. Then the actual two-party vote share would be 38/78 = 48.7%. Thus, this question would resolve as 48.7-44.4 = 4.3. Conversely, if Trump's vote share was lower than FiveThirtyEight's prediction, the question would resolve as a negative value.

The forecast will be taken from the latest forecast on the day before the election, i.e. November 2. If FiveThirtyEight does not display a forecast at that time, or it has not been updated in more than a week, this question resolves ambiguous.

FiveThirtyEight's "popular vote" forecast is currently displayed on their 2020 election forecast page in a tab under the "How the forecast has changed" section. Should the formatting change, the forecast that displays this same information will be considered as the popular vote forecast. If there is ambiguity, the admins will decide what forecast is the reference forecast for this question.

If Donald Trump or Joe Biden cease to be their respective parties' nominees for the 2020 US presidential election, this question resolves as ambiguous.

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