Biden’s lead in the average has never gotten below 4 or 5 points or above 10 points. That’s a remarkably narrow range.
If you were to construct a 95% confidence interval around individual polls, Biden’s advantage in any individual poll has been within 6.5 points of that 7 point average.
A look at the previous 19 elections since 1940 reveals that the average range has been double that from January of the election year through early September of the same year. That is, the range in the polls in the average election has been closer to 14 to 16 points, depending on how you calculate the polling average.
In fact, the same gyrations in the polls were present the last two times incumbents lost. Gerald Ford went from easily winning in 1976 to being down by a wide margin and ultimately losing by 2 points. Jimmy Carter’s advantage evaporated during the early months of 1980, but he was able to close a double-digit deficit to Ronald Reagan in the late summer of that year. Eventually, Reagan won by 10 points.
This year, despite at least as many unforeseen events as the 1980 campaign, has featured none of that wild movement.
Clinton’s edge at this point in 2016 was only about 3 points. Biden’s is more than double that.
The difference, of course, is that many polls didn’t actually have Obama ahead nationally because his average lead was so narrow.
That is, Biden’s lead in the state that would provide him with the 270 electoral votes is closer to 5 points than 8 points.
And given that there is still time for Biden’s national lead to shrink to 6 points or even 5 points, he can’t take this election to the bank by any stretch.
Still, the safest bet at this point is that Biden has been ahead and will likely be ahead when all the votes are counted.