Before the U.S. election, Trump trailed Hillary Clinton by only about 2 percentage points in the average swing state.1 In the Brexit vote, the “Remain” campaign’s lead was at least as narrow: about 2 points according to a simple average of polls, or just 0.5 percentage points according to a more complex averaging method. So while Trump’s victory and Brexit were historic events in world history, they were utterly routine occurrences from a polling standpoint; 2- or 3-point polling errors are extremely common.
But while there were plenty of precedents for a polling error large enough to elect Trump, there aren’t all that many examples of a 26-point polling error, which is what Le Pen would need. Pundits and other political observers often have poor intuition when it comes to translating polls into probabilities, leading them to treat narrow, fragile leads the same as double-digit ones. Ironically, the same type of sloppy thinking that led people to underestimate the chances for the Trump and Brexit victories may lead them to overestimate Le Pen’s odds.
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