Last month, the American Association for Public Opinion Research released a very careful look at the polls’ performance in 2016 here. The committee began its work in the spring of 2016, intent on examining the accuracy of the 2016 primary and general election pre-election polls and the different methodologies pollsters used. State-level general election polls did not do as well. National and state polls underestimated support for Trump, but in 2000 and 2012, general election polls underestimated support for the Democratic presidential candidate. In 2016, the polls pointed to the winner in 86 percent of the 78 primaries based on state polling averages.

Source: Forbes June 19, 2017 14:48 UTC