Some saw the 2016 election as an upset but many indicators hinted at a Republican win.
The 2016 presidential election was not a good year for pollsters. Most anticipated a strong Clinton win in both the popular and the Electoral College vote, precipitating a lot of subsequent discussion about why polls performed so poorly in this election. There are a number of possible reasons. First, polling needs random samples of people who will vote, and this may be getting harder to do. Second, in this election people may have been reluctant to give their true views. Third, people's views may simply have been unstable over time. Whatever the case, polls did not do that well.
The 2016 presidential election was not a good year for pollsters.
An alternative approach to predicting presidential elections is to look at the fundamental forces driving people's voting behavior. This is the approach I take in my election work. The approach does not take polling data into account. It does not ask people how they are going to vote, but tries to explain what motivates them to vote the way they do.
Using econometric methods and data extending back to 1916, I have found four conditions that affect votes for president. The first is whether the president is running again. If so, this has a positive effect on votes for the president. The second is how long a party has controlled the White House. Voters like change; when a party has been in power for two or more consecutive terms, this has a negative effect on votes for that party's candidate. The third is the slight but persistent bias in favor of the Republican Party.