Assessing the Swing States and Explaining Margin of Error

In a feature published in Wednesday's paper, the Wall Street Journal pinpointed the six swing states that will be the most competitive in 2020: Arizona, Florida, Michigan, North Carolina, Pennsylvania, and Wisconsin. Conveniently, CNBC and Change Research just released poll results from these six states.

Former Vice President Joe Biden leads in three states and President Donald Trump in two. The candidates are tied in one. Here are the full results:

  • Arizona: Trump 45%, Biden 44% (Trump +1)
  • Florida: Biden 48%, Trump 45% (Biden +3)
  • Michigan: Biden 48%, Trump 46% (Biden +2)
  • North Carolina: Biden 46%, Trump 45% (Biden +1)
  • Pennsylvania: Trump 50%, Biden 46% (Trump +4)
  • Wisconsin: Trump 45%, Biden 45% (tie)

The margin of error for the poll is plus/minus 1.56%. That means that in Wisconsin, a result of Trump 46.56% vs. 43.44% (or vice versa) is within the realm of possibility. This is why most political analysts do not see polls showing leads of fewer than five points as particularly informative. Even sustained but small leads have proven useless in the 2016 presidential election (especially in Michigan and Pennsylvania) and in 2018 in Florida.

In this poll, the only state that is outside the margin of error (i.e., statistically significant) is Pennsylvania. No matter how you manipulate the numbers, the best possible result for Biden with this sample is 48.44% for Trump and 47.56% for Biden -- a net deficit. This is good news for the president, as the Keystone State has 20 votes in the Electoral College.

However, the Trump campaign should heed this warning from Change Research: "Across the six battleground states Trump won in 2016, Biden now leads by 1 point (47% Biden, 46% Trump). This is a 3 point shift in the margin since our last wave and the first time Biden has led." Biden leads by seven points nationally, 48% to 41%, with a margin of error of 2.57%.

Other polls have shown Trump leading in the swing states. As I reported on May 13th, a CNN poll shows "Trump lead[ing] in battleground states -- defined as 'Arizona, Colorado, Florida, Georgia, Maine, Michigan, Minnesota, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia, and Wisconsin' -- by seven points: 52% to 45%."

For reference, my Electoral College map has Biden winning Arizona, Michigan, and Pennsylvania and Trump winning Florida, North Carolina, and Wisconsin. This is subject to change if more polls show the same results as Change Research.

Point of clarification: The 1.56% margin of error is either for the entire battleground state sample or a catchall which is applicable for each state surveyed. My analysis is predicated upon the latter assumption.

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