Silver says that the polls really were pretty reliable and the main problem is that some people refused to accept that Trump actually could win. Sample quote:
We also received a lot of criticism from Democratic partisans in the closing weeks of the campaign — more than we did from Trump supporters — because they thought we didn’t have Clinton as a heavy enough favorite. That’s unusual. We’ve forecasted enough races over the years to have taken criticism from almost every side. But in the past, it’s always been the trailing candidate’s supporters who gave us more grief.
In this respect, there’s another parallel between Trump’s victory on Tuesday, and the United Kingdom’s vote to leave the European Union in June. Brexit polls showed the race almost tied, with “Remain” leading by perhaps half a percentage point. In fact, “Leave” won by about 4 percentage points. The polls took a lot of criticism even though they’d shown “Leave” at almost even-money, whereas betting markets — and the conventional wisdom from London-based reporters — had “Remain” heavily favored to prevail. Londoners may have interpreted the data in selective ways because of the “unthinkability” of Britain’s leaving the EU to people in their social circles.
Tuesday’s results were similar. We strongly disagree with the idea that there was a massive polling error. Instead, there was a modest polling error, well in line with historical polling errors, but even a modest error was enough to provide for plenty of paths to victory for Trump. We think people should have been better prepared for it. There was widespread complacency about Clinton’s chances in a way that wasn’t justified by a careful analysis of the data and the uncertainties surrounding it.
