I asked about the failure of the polls in this years presidential election. Her explanation: The polls are looking at future events but are biased by the past. The various companies and institutions adjust the polls they do by looking at their past prognoses and the real results of the past event. They then develop correcting factors, measured from the past, and apply it to new polls. If that correcting factor is wrong, possibly because of structural changes in the electorate, then the new polls will be corrected with a wrong factor and thus miss the real results.

Polls predicting the last presidential election were probably off by 3 or 5 points towards the Republican side. The pollsters then corrected the new polls for the Clinton-Trump race in favor of the Democratic side by giving that side an additional 3-5 points. They thereby corrected the new polls by the bias that was poll inherent during the last race.

But structural changes, which we seem to have had during this election, messed up the result. Many people who usually vote for the Democratic ticket did not vote for Clinton. The "not Clinton" progressives, the "bernie bros" and "deplorables" who voted Obama in the last election stayed home, voted for a third party candidate or even for Trump. The pollsters did not anticipate such a deep change. Thus their correction factor was wrong. Thus the Clinton side turned out to be favored in polls but not in the relevant votes.