In his final outlook for the presidential race, Nate Silver of Five Thirty Eight gives Hillary Clinton a 71 percent chance of winning the election.

He has Clinton leading by 3.6 percentage votes in the popular vote by a 302-235 margin in the Electoral College, though he cautions that the night could play out in several different ways. Five Thirty Eight actually favors Clinton to win 323 votes across the electoral map, including all the states President Obama won in 2012 except Ohio and Iowa. But Clinton’s lead in Florida and North Carolina are so tenuous that Silver put the likely outcome at 302, with the Democratic nominee winning Florida or North Carolina, but not both.

Here are some of the statistics guru’s observations, updated six hours ago, as we head toward the first poll closures:

… So what’s the source of all the uncertainty? And why does the same model that gave Mitt Romney only a 9 percent chance of winning the Electoral College on the eve of the 2012 election put Trump’s chances about three times higher — 28 percent — this year? It basically comes down to three things:

  • First, Clinton’s overall lead over Trump — while her gains over the past day or two have helped — is still within the range where a fairly ordinary polling error could eliminate it.
  • Second, the number of undecided and third-party voters is much higherthan in recent elections, which contributes to uncertainty.
  • Third, Clinton’s coalition — which relies increasingly on college-educated whites and Hispanics — is somewhat inefficiently configured for the Electoral College, because these voters are less likely to live in swing states. If the popular vote turns out to be a few percentage points closer than polls project it, Clinton will be an Electoral College underdog.

… The track record of polling in American presidential elections is pretty good but a long way from perfect, and errors in the range of 3 percentage points have been somewhat common in the historical record. Of note, for instance, is that Obama beat his national polling average by nearly 3 points in 2012, although state polls did a better job of pegging his position. In 2000, Al Gore was behind by about 3 points in the final national polling average but won the popular vote. In 1996, Bill Clinton was ahead in national polls by about 12 points, but won by 8.5.

Nate Silver

Silver

In three of the last five presidential elections, in other words, there was a polling error the size of which would approximately wipe out Clinton’s popular vote lead — or alternatively, if the error were in her favor, turn a solid victory into a near-landslide margin of 6 to 8 percentage points. There’s also some chance of a larger error still. In 1980, Ronald Reagan led in final national polls by slightly less than Clinton does now, but wound up winning the popular vote by almost 10 percentage points.

Three- or 4-point polling errors should also be familiar from other contexts. Republicans beat their polls by 3 or 4 percentage points, on average, in competitive Senate and gubernatorial races in the 2014 midterms. Brexit was about a 4-point polling error, and the error in the 2015 U.K. general election was larger — Conservatives’ margin over Labour was understated by about 6 percentage points. We often get annoyed when people express shock after outcomes like these occur — polling is a tricky business — only to expect polls to be infallible the next time around.

…Undecided voters contribute significantly to uncertainty in the FiveThirtyEight forecast. If there were half as many undecideds — in line with recent past elections but still more than in 2012 — Clinton’s chances of winning the Electoral College would rise to 78 percent in our forecast, and her chances of winning the popular vote would be 89 percent, higher than Obama’s were in our final 2012 forecast.

Perhaps the most intriguing prediction by Five Thirty Eight is that Michigan ranks third among all states, even slightly higher than North Carolina, in the likelihood of emerging as the tipping point in the election. Michigan’s chances are at 11.7 percent, behind only Florida and Pennsylvania. Silver forecasts a Clinton margin in Michigan of 4.2 points. The Clinton camp is counting on wins in Pennsylvania and Michigan so their prospects of acting as a tipping point would be in the event of Election Night surprises in Trump’s favor.

The Five Thirty Eight forecasts, or “probabilities,” come from simulating the election 20,000 times, which produces a distribution of possible outcomes for each state.

 

 

Recent Posts: