538 Model Megathread

[Erich Maria Remarque]

Haha, Lief will be pleased.

In the video, Nate is saying that Trump has doubled this chances in two weeks and then add... that the tightening is coming mostly from nationall polls and trackers and automated or online states polls and that those are not a gold standard.

It really feels to me like he is saying: Don't blame me, blame the goddamn trackers

http://fivethirtyeight.com/features/trumps-chances-of-victory-have-doubled-in-the-last-two-weeks/?ex_cid=2016-forecast

[ursulahx]

Now I think about it, when Silver went on a mini-rant during a recent podcast, emphasising how big he thought Trump's chance of winning was, he sounded genuinely scared. I wonder if he sees it as part of his mission to get Democrats to take the threat seriously and go out and vote. If so, I can't help feeling there are better ways of doing it.

[elcorazon]

Now I think about it, when Silver went on a mini-rant during a recent podcast, emphasising how big he thought Trump's chance of winning was, he sounded genuinely scared. I wonder if he sees it as part of his mission to get Democrats to take the threat seriously and go out and vote. If so, I can't help feeling there are better ways of doing it.

he's a freedom fighter

[Brittain33]

With Iowa and Ohio leaning Trump and Indiana and Missouri solidly Republican, where we're headed is a scenario where the Midwest votes like it's 2004 and everywhere else votes like it's 2008.

[rafta_rafta]

Now I think about it, when Silver went on a mini-rant during a recent podcast, emphasising how big he thought Trump's chance of winning was, he sounded genuinely scared. I wonder if he sees it as part of his mission to get Democrats to take the threat seriously and go out and vote. If so, I can't help feeling there are better ways of doing it.

He applied punditry over his own model's numbers during the primary and is now overcompensating for it. The model is still accurate IMO

[The Other Castro]

Now I think about it, when Silver went on a mini-rant during a recent podcast, emphasising how big he thought Trump's chance of winning was, he sounded genuinely scared. I wonder if he sees it as part of his mission to get Democrats to take the threat seriously and go out and vote. If so, I can't help feeling there are better ways of doing it.

He applied punditry over his own model's numbers during the primary and is now overcompensating for it. The model is still accurate IMO

The model is accurate for what would be implied by some of the polls inputted. The problem is that most of the polls we've gotten recently are trash so they have a much greater say in the result.

[Mr. Morden]

Now I think about it, when Silver went on a mini-rant during a recent podcast, emphasising how big he thought Trump's chance of winning was, he sounded genuinely scared. I wonder if he sees it as part of his mission to get Democrats to take the threat seriously and go out and vote. If so, I can't help feeling there are better ways of doing it.

He applied punditry over his own model's numbers during the primary...

Not really.  He didn't have a model during the primaries.  The reason being, as he put it, modeling the primaries is too difficult.  Once we were deep into the primaries, he made some toy models based on the demographics of people who had voted so far, but by that time he was acknowledging that Trump was the favorite.

[rafta_rafta]

Now I think about it, when Silver went on a mini-rant during a recent podcast, emphasising how big he thought Trump's chance of winning was, he sounded genuinely scared. I wonder if he sees it as part of his mission to get Democrats to take the threat seriously and go out and vote. If so, I can't help feeling there are better ways of doing it.

He applied punditry over his own model's numbers during the primary...

Not really.  He didn't have a model during the primaries.  The reason being, as he put it, modeling the primaries is too difficult.  Once we were deep into the primaries, he made some toy models based on the demographics of people who had voted so far, but by that time he was acknowledging that Trump was the favorite.

He didn't have a overall prediction model like the presidential race but he did have a per state model which took into account all the polls done for the state. And those numbers were right almost all the time and they predicted that Trump will take all the states that he did.

What he didnt account was the momentum that Trump gained from the lead and that the rest of GOP base eventually coalesced around him

[Mr. Morden]

He didn't have a overall prediction model like the presidential race but he did have a per state model which took into account all the polls done for the state.

He didn't roll that out until around Christmas time, by which time he was already saying that Trump had a good chance of winning the nomination, if not the favorite.  Most of the "Trump can't win" comments he made were back in the summer / early fall of 2015, before he had any such model.

[Crumpets]

Now I think about it, when Silver went on a mini-rant during a recent podcast, emphasising how big he thought Trump's chance of winning was, he sounded genuinely scared. I wonder if he sees it as part of his mission to get Democrats to take the threat seriously and go out and vote. If so, I can't help feeling there are better ways of doing it.

He applied punditry over his own model's numbers during the primary...

Not really.  He didn't have a model during the primaries.  The reason being, as he put it, modeling the primaries is too difficult.  Once we were deep into the primaries, he made some toy models based on the demographics of people who had voted so far, but by that time he was acknowledging that Trump was the favorite.

He didn't have a overall prediction model like the presidential race but he did have a per state model which took into account all the polls done for the state. And those numbers were right almost all the time and they predicted that Trump will take all the states that he did.

What he didnt account was the momentum that Trump gained from the lead and that the rest of GOP base eventually coalesced around him

And of course let's not forget his endorsement tracker model.

[muon2]

What is the uncertainty of the model, given the # of simulations they run?  That is, each time they enter new polls, they apparently run 10,000 simulations based on the latest #s, and that produces (among other things) an overall projected vote margin and win probability.  But let's say they then ran *another* 10,000 simulations with the same input #s but a different random seed?  How different would the results be?  Because if they'd be different, then in theory you could put in a favorable poll for one candidate and it would end up "helping" the other candidate, just because of simulation noise.  But I'm assuming that 10,000 is enough for the simulation noise to be small?

This is purely a statistical noise effect; given Clinton's win percentage of 70% or so, we shouldn't be surprised by jumps of 0.6% or so in Clinton's win percentage just from rerunning the simulations (1 sigma).  If you start looking at individual battlegrounds, we definitely shouldn't be surprised if one of them jumps a percent or two just from statistical noise.

I wouldn't have expected changes that significant with 10,000 trials, although I will say my technical experience in statistics is fairly limited.

Statistical noise scales as 1 / sqrt(number of trials), so it takes a lot of trials to get your error below the percent level.  To decrease your statistical error by a factor of 10, you need to run your simulation 100 times longer.

This does mean that 538 really shouldn't be listing the percentage points on their probabilities, unless they feel like running a million simulations each time.

With 10K trials and a 50% expected value the estimated standard error is 0.5%, for a 20% (or 80%) expected value the estimated standard error is 0.4%. For a technical paper they should include the decimal on their percentage results, but also quote the standard error as 0.5% (or less for percentages away from 50%). However, if the intend the user to interpret the error as a margin of error then that is 1.98 times the standard error. In that case they should not use the decimal and report the value as a whole number percentage. Since polling and journalists tend to assume a margin of error then whole number percentages would be preferred.

[Mr. Morden]

He didn't have a overall prediction model like the presidential race but he did have a per state model which took into account all the polls done for the state.

He didn't roll that out until around Christmas time, by which time he was already saying that Trump had a good chance of winning the nomination, if not the favorite.  Most of the "Trump can't win" comments he made were back in the summer / early fall of 2015, before he had any such model.

To follow up on the above: I just dug up the blog post in which Nate announced the primary forecasts.  Looks like it started on Jan. 12, 2016:

http://fivethirtyeight.com/features/how-we-are-forecasting-the-2016-presidential-primary-election/

By that time he was no longer saying that Trump was doomed.  At the time that he was saying Trump was doomed, he didn't have any model.

[Moderate Pennsylvanian]

I don't understand. With the latest update, Clinton dropped from 69.0 to 67.6 in polls-only. The only addition was a poll showing Trump +9 in Missouri and it is only the seventh-highest-weighted Missouri poll.

[Erich Maria Remarque]

I don't understand. With the latest update, Clinton dropped from 69.0 to 67.6 in polls-only. The only addition was a poll showing Trump +9 in Missouri and it is only the seventh-highest-weighted Missouri poll.

Lol, it does look ridiculous! They probably make much fewer simulation during "quick" adding of the poll. But once in while perform a real 10k-simulations test.

[Slander and/or Libel]

10k simulations only takes a couple of minutes.

[100% pro-life no matter what]

Nevada flips in the nowcast, as Trump passes 70% in Iowa, his first Obama state at that level.  For TNVol's sake, New Hampshire is now more competitive than Iowa.

[Nyvin]

In polls-plus the Democrats have a better chance to take the Senate than Hillary does of winning the White House.   I find that kind of funny.

[Attorney General, LGC Speaker, and Former PPT Dwarven Dragon]

Looking at the 538 model is quite comforting. While Atlas and the media are screaming about a tightening race, Silver shows the truth: While a number of states are quite shaky at the moment, Clinton has 272 electoral votes - enough to win - still solidly behind her. Clinton's chances are at least 71.5% in every single state in the firewall.

[Erich Maria Remarque]

The main question is if we are now at

a) new equlibrium
b) Trump still gaining
c) Clinton regaining

We'll find out soon. But right now look at that big, beutiful Now-Cast. And Mexico Nate Silver will pay for it.

[Figueira]

The new California poll caused North Carolina and Florida to switch places.

[Meclazine for Israel]

Donald Trump at 240
Hillary Clinton at 296

North Carolina, Florida and Nevada looking like a dead heat according to 5-38.

Things getting interesting if Donalds' momentum continues. Especially in these states and Colorado.

[Middle-aged Europe]

Polls-only at 66.6% right now.

The prediction from HELL!!

[jaichind]

For Polls plus the addition of the AZ Saguaro Strategies poll which had Clinton +1 which got adjusted to Trump +1 actually increased Trump's chances from 34.1 to 34.4 which seems bizarre to me given where Trump should be for AZ.  Only reason I can think of is that this poll is slight more positive for Trump than the prev Saguaro Strategies poll had Clinton +2.

[Mr. Morden]

For Polls plus the addition of the AZ Saguaro Strategies poll which had Clinton +1 which got adjusted to Trump +1 actually increased Trump's chances from 34.1 to 34.4 which seems bizarre to me given where Trump should be for AZ.  Only reason I can think of is that this poll is slight more positive for Trump than the prev Saguaro Strategies poll had Clinton +2.

Again, shifts of about half a percent are totally meaningless, given that it's based on 10,000 simulations.  You can take the exact same set of polls and run them in a second set of 10,000 simulations, and you'll get, on average, a shift of about half a percent in Clinton's win probability.

[Blackacre]

Update: New Hampsire is out of the freiwal.

I defined the Freiwal as the states that always seem to have a better chance of being carried by HRC than the election according to 538. New Hampshire was among them, but now thanks to Trump leading in a couple polls, it is not