538 model & poll tracker thread

[Smash255]

It's miniscule but I really dont understand:

Before YouGov poll: Biden +8.3

YouGov poll which has +11 (RV) and +9 (LV) tabs

Biden's lead ticks *down* to 8.2.

How did it tick down when the poll result was *above* the previous average?

They also extrapolate state poll data into their national #'s, so if there was some state poll data showing better results for Trump released around the same time  it might have canceled out the increase from a good national poll.  Older national polls or even older state polls that were strong for Biden receiving less weight could have been a factor as well.  They are now at 9.2 as of this morning

[Smash255]

Recent positive polling for Biden in Minnesota took his win % from 69% to 82% in just under two weeks. Wisconsin also has also had a similar bounce from 66% to 77%.

Do we know if any of this is also due to the calendar slipping away from Trump? The polls have stayed quite constant, even Florida has been about +3 for a month now, so it would seem that the closer to the election, the less uncertainty there is, and Silver has admitted that the uncertainty is what is boosting Trump's chances the most.

Yeah that is part of it.  The polling average has moved slightly in Biden's direction in both states.   Also the Economics and Incumbency based projection does favor Trump, but as we get closer to the Election that makes up less of the forecast.

[Smash255]

Today we had three national polls which showed Biden ahead by 12, 10, and 9 points.
And yet 538's aggregate remains stuck at 7.5. I don't know about you but this starts to look absurd to me.

One thing to keep in mind is 538's national polling #'s calculation combine national and state polls

[Smash255]

Today we had three national polls which showed Biden ahead by 12, 10, and 9 points.
And yet 538's aggregate remains stuck at 7.5. I don't know about you but this starts to look absurd to me.

One thing to keep in mind is 538's national polling #'s calculation combine national and state polls

I think it's the model that takes under consideration state polls, not the national polling aggregate.

From the pollster page

Polling averages are adjusted based on state and national polls, which means candidates’ averages can shift even if no new polls have been added to this page.

[Smash255]

Today we had polls showing Biden ahead by 10, 9, and 8 points, and the needle remained stuck at 7.1. I guess Silver's model doesn't consider them as high quality as HarrisX and Rasmussen.

Today's USC Dornsife poll replaced yesterday's. +9.5 to +10, a half point change on a B/C rated pollster.

Today's Redfield & Wilton Strategies poll replaced last week's. +7 to +9, a two point change on an unrated pollster.

Today's Ipsos poll replaced last week's. +9 to +8, a one point decline on a B- rated pollster.


So three new low- to mid-grade national polls showing minor or even negative changes get fed into a trendline with dozens of other polls from dozens of other pollsters. The model did exactly what you should expect it to do.

In addition state polls feed more into the national poll averages than the national polls themselves do.

[Smash255]

It’s getting a little bit creepy how stable the model is right now.  Biden has been at 77 for 7 straight days.  It seems like there should be a little movement just by random chance.  I’m surprised Nate isn’t tweeting worries about herding yet.

The model assumes pretty strong convention bounces that last for up to a month.  Next week could be significant as I believe that's when Trump's assumed bounce finally goes to 0.  The narrowing to Biden being only a 2:1 favorite in late August was because the model assumed a DNC polling bounce that didn't really materialize.  I have a feeling it's overweighting the RNC as well and perhaps giving Biden too much credit right now.

I don't think the bounces are meant to last that long, where have you seen that?  The tightening in mid-August was because Trump was getting an RNC bounce and Biden wasn't getting a DNC bounce.

It does seem like the model is still adjusting all of Trump's polling averages down by about a half point to compensate for assumed residual convention bounce.

This part is true.  The amount of the adjustment depends on the amount of polls and when.  A state that had a bunch of polls in early September and only a couple in the last week or so will generally have a larger adjustment than a state with a bunch of recent polls.   As more recent polls come out the adjustment gets lessened.   

[Smash255]

Today we had polls showing Biden ahead by 10, 9, and 8 points, and the needle remained stuck at 7.1. I guess Silver's model doesn't consider them as high quality as HarrisX and Rasmussen.

Today's USC Dornsife poll replaced yesterday's. +9.5 to +10, a half point change on a B/C rated pollster.

Today's Redfield & Wilton Strategies poll replaced last week's. +7 to +9, a two point change on an unrated pollster.

Today's Ipsos poll replaced last week's. +9 to +8, a one point decline on a B- rated pollster.


So three new low- to mid-grade national polls showing minor or even negative changes get fed into a trendline with dozens of other polls from dozens of other pollsters. The model did exactly what you should expect it to do.

In addition state polls feed more into the national poll averages than the national polls themselves do.

They feed the model, not the polling aggregate.

Right on the polling page it states national and state polls feed into the aggregate.

[Smash255]

Right on the polling page it states national and state polls feed into the aggregate.

It must be a mistake. The aggregate moves only with national polls. Just watch it.
OTOH, it's very clear that his model is swayed heavily by state polls.

This is directly from the national polling page

Polling averages are adjusted based on state and national polls, which means candidates’ averages can shift even if no new polls have been added to this page

[Smash255]

This model has become completely perplexing to me. 

On Sept. 19, 11 days ago, Biden was 77% to win.
During the past 11 days, the following things have happened:
1.) Biden’s national lead has grown a full percentage point, from 6.6 to 7.6
2.) There have been three A or A+ quality polls of the tipping point state (PA) suggesting Biden is winning the state by more than his national lead
3.) The election has gone from being 45 days away to 34 days away, which should substantially reduce uncertainty.

And yet Biden’s win % has only increases a single point, to 78%.
How is this possible?  What is actually necessary to move the needle?

The main issue seems to be that Biden was being artificially propped up because the model thought the RNC convention bounce was still going on at that point (kind of weird that they modeled such a long convention bounce, but I guess they're basing themselves off previous cycles when this stuff had more of an impact). Now, that bounce adjustment has almost entirely worn off, which has had the effect of blunting Biden's gains.

Even then, these gains are far from uniform. He's continued to get bad polls in FL, NC and AZ, which while not the most likely tipping points, would be a major freiwall for Biden if he could pull away there.

In the model they did state that the Convention bounce they were adding were going to be less than normal, though the GOP one would last longer due to the timing of it being second.  Also even if the bounce itself was 10-15 days or so keep in mind the polls in with the average will be a bit longer than that.

[Smash255]

538 avg PA before Q-pac: Biden +5.2
After Q-pac: Biden +5.2

Huh?

Also, Trump getting +1 in Iowa, despite it being his only recent lead of the last 8 polls in 538s forecast, jumped IA to 54% Trump 46% Biden. Joke.

Keep in mind that while 538 doesn't remove a poll when the same pollster comes out with another poll it will receive less weight.

In the case of PA, the previous QU poll was Biden +8, a Biden +7 poll from them really isn't going to cause any shift.

In Iowa, the previous QU poll was Biden +5, so that poll is now weighted a bit less since a new QU poll is out. 

[Smash255]

I want single digits by Tuesday!

Why wait? He's already down to a 9.96% chance right now.

Where can you see it down to that level?

If you download the model outputs at the bottom of the page and open up national toplines from that dataset into excel.   It is up to 10.03% as of this morning

[Smash255]

Worth noting that even after the Selzer poll, Biden is still at 90% to win. (And wait — if polls were “exactly as wrong as 2016,” wouldn’t Biden be winning Texas?)

It did tick down  to 89 after the Seltzer poll came out, but after the FL & PA WAPO polls and the economic index going down slightly more it went back up to the 90% mark