The polls have failed again. They gave Joe Biden a 6.9 percentage point lead in national voting intent, according to the average of various polls conducted by the U.S. political news website Real Clear Politics. And Donald Trump surprised again on Tuesday by turning the polls around and achieving a valuable victory in Florida that opens the door to reelection.

In the previous campaign, the candidate Hillary Clinton led all the polls averages. The truth is that the victory of the magnate in 2016 was a real surprise that was not predicted in the opinion polls of the country. Virtually only one conservative pollster predicted that Trump would be the president of the United States.

Nationally, the polls worked well, stipulating that Clinton had a 3 percentage point lead in the national popular vote and eventually won the national vote by 2 percentage points. So, in reality, it wasn’t an industry-wide mistake. Nevertheless, in the U.S. you don’t get to the presidency by number of votes, but by the so-called Electoral College.At the state level, the polls did have a historically bad year: undecided voters (people who made a decision in the last week) did so for Trump by large margins. In key states like Wisconsin and Florida, voters who made a late decision to vote for Trump did so by double-digit margins, and the polls did not measure that late change.

Another problem was a technical error. Most state pollsters did not ensure that their samples were representative of the level of voter education. It is well known that college graduates are more likely to take surveys than those with less formal education. And that’s fine as long as they statistically adjust their survey (in a process called weighting) to make sure that college students are not overrepresented.


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