I would note that the gap is a little bit narrower in our *forecast*: Biden +5.1 in Pennsylvania vs. +7.8 in the national popular vote. https://projects.fivethirtyeight.com/2020-election-forecast/">https://projects.fivethirtyeight.com/2020-elec... https://twitter.com/mattyglesias/status/1320814481782513666">https://twitter.com/mattygles...

Why is Biden +9.1 in our national poll average but +7.8 in our forecast?

* The forecast still assumes just a teensy bit of tightening (about 0.4 points toward Trump)
* The forecast is mostly based on state polls, which have been more consistent with an ~8 point lead than 9-10.

Why this state/national poll gap exists is an interesting question. Also there have been points in the year where it seemed to run in the opposite direction, e.g. before the first debate, our model thought Biden led by ~8 points from state polls vs. a ~7 point national poll lead.

FWIW, the current implementation of our model is sparing with how it uses national polls. You could argue for moving Biden& #39;s state polls upward slightly so that they better match the national polls. Our 2012 & 2016 models did that to some degree, but this year& #39;s does not really.