The most accurate polling every election is Investors Business daily. They say Trump will win. Checkmate liberals.
They are not the most accurate pollster every election.What you posted is an average of the last 3 elections.In 2012 they were not the most accurate being 2.3% off while 3 other polls were closer.
1.This might not be their final poll and thats the one that gets graded in your comparison. 2.In their previous 3 polls the results were from head to head match ups with no third parties.In this years head to head match up poll it has Hillary +1
@peilthetraveler are you trying to create an empirical correlation based on 4 data points ? I would advise you statistics 101 and spurious correlations: https://www.youtube.com/user/BCFoltz and http://tylervigen.com/spurious-correlations