Why 2016 election polls missed their mark
Three senior researchers from the Pew Research Centre suggest three possible reasons why US polls failed to predict the outcome of the 2016 Presidential election, including: nonresponse bias: which occurs when certain kinds of people systematically do not respond to surveys despite equal opportunity outreach to all parts of the electorate; "shy Trumpers" suggests that support for Trump was socially undesirable, and that his supporters were unwilling to admit their support to pollsters; and the way pollsters identify likely voters: because voting is non compulsory in the US, pollsters can't know in advance who is actually going to vote, so they develop models predicting who is going to vote and what the electorate will look like on election day.