In national and state-level polls tended to under-estimate support for Trump, the Republican nominee. Additional topics on election polling A number of Pew Research Center publications provide additional examples of how election polls are conducted and used.
Pollsters that are banned by FiveThirtyEight because we know or suspect that they faked their data are not included in the averages. Wisconsin polls exhibited the largest average signed error 6.
Presidential primary polls generally performed on par relative to past elections.
In states like Michigan, Wisconsin and Florida where Trump was listed first on the ballot state-wide, this order effect could have slightly boosted his support in the election relative to the polls BBC News ; Pasek ; Gelman Pollsters get half-credit if they show a tie for the lead and one of the leading candidates wins.
Source — Figures for to computed from data made public by FiveThirtyEight.