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Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

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Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#171

Post by sjy »

ta8645 wrote: post #115
cwhiz wrote: post #28

Not sure if it’s wrong to put this here, but here is a link to their election forecast. https://projects.economist.com/us-2020-forecast/president You can compare this to the 538 model and see where these two teams and forecasts disagree.

Can someone help me understand what odds like this mean in the context of an election? The model says that Trump has a 1 in 10 chance of winning. With a fair 10-sided die it makes sense that you have a 1 in 10 chance of any given side rolling face up. But what is the die that is being rolled in these election statistics? What is the "chance" element that is being predicted?

> what is the die that is being rolled in these election statistics?

A program which randomly generates outcomes for each state, based on probability distributions inferred from the polls, and calculates who wins the election given those outcomes. They run the program repeatedly and report the proportion of simulated wins as the probability of winning. https://en.wikipedia.org/wiki/Monte_Carlo_method

Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#172

Post by artichokes »

TTPrograms wrote: post #147

For a post on a blog presumably focused on statistics the author seems oddly concerned with a model that predicts odd events as being "possible". The difference between "possible" and "impossible" is \eps Likewise asserting that California with a 3% chance of going Trump is absurd is an unreasonable degree of overconfidence. Assuming maximizing expected return, the author is implying that they would be willing to tak…

I don't know if I'm reading your comment wrong but I would happily take that bet- I think most people would. Want to make it? The election result of California isn't a matter of probability; it's an empirical matter that the number of people who will vote for Biden in California far exceeds the number that will vote for Trump.

Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#173

Post by Der_Einzige »

TTPrograms wrote: post #147

For a post on a blog presumably focused on statistics the author seems oddly concerned with a model that predicts odd events as being "possible". The difference between "possible" and "impossible" is \eps Likewise asserting that California with a 3% chance of going Trump is absurd is an unreasonable degree of overconfidence. Assuming maximizing expected return, the author is implying that they would be willing to tak…

I'll take that exact bet for you. I like those odds because I know that the chance of california going red is effectively 0

Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#174

Post by dragonwriter »

StreamBright wrote: post #164
ta8645 wrote: post #115

Earlier quoted context omitted.

Can someone help me understand what odds like this mean in the context of an election? The model says that Trump has a 1 in 10 chance of winning. With a fair 10-sided die it makes sense that you have a 1 in 10 chance of any given side rolling face up. But what is the die that is being rolled in these election statistics? What is the "chance" element that is being predicted?

It pretty much means nothing. These sort of models produced wrong result again and again. For me the biggest question mark if that if we know that recent (last 5) elections were very close how can you predict somebody winning with 93% chance? Maybe I do not understand something here.

> These sort of models produced wrong result again and again

IIRC, 538s election models (house, Senate, and Presidential) have been quite accurate in aggregate.

Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#175

Post by sequoia »

As a US voter I am very frustrated With and tired of this obsession with election forecasting. Is it going to influence whether or not you go out and vote? If not, what is the point of it?

What value does something like fivethirtyeight add to our democracy, if any? Is this motivation the same as that of diving deep into baseball stats or Star Wars starship engineering, just like “nerding out” for its own sake?

Contrast the voter who never looks at any of these polls with one who keeps up with them daily. Is the latter voter better off in some way? Is this just about trying to read the tea leaves so you can strut and preen later about having been correct, should the dice roll be in your favor?

My concern is that these things are distracting and may actually dissuade some people from voting because they think they “don’t have to.”

Here’s an idea: everyone go vote for whoever you think the best candidate is regardless of what a stack of polls say.

Someone set me straight here, what is the point of all this stuff.

Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#176

Post by ncw96 »

sequoia wrote: post #175

As a US voter I am very frustrated With and tired of this obsession with election forecasting. Is it going to influence whether or not you go out and vote? If not, what is the point of it? What value does something like fivethirtyeight add to our democracy, if any? Is this motivation the same as that of diving deep into baseball stats or Star Wars starship engineering, just like “nerding out” for its own sake? Contra…

> What value does something like fivethirtyeight add to our democracy, if any?

One possible use of polls and election models is for helping people who want to donate to candidates determine which races are closest and where their money is most likely to have an impact.

> Here’s an idea: everyone go vote for whoever you think the best candidate is regardless of what a stack of polls say.

Because the US does not have ranked choice voting in most elections, polls are useful to determine which candidates are viable. If your preferred candidate is only polling at 5%, they are pretty unlikely to win, so you might want to vote instead for whichever of the leading candidates you find most agreeable.

Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#177

Post by i_love_limes »

preommr wrote: post #8

> It didn't take very long to do the analysis. But it did then take another hour or so to write it up. It's very interesting to see how long it takes people to do things. I am amazed that entire article took 1 hour to type up. I've spent entire afternoons trying to write shallower pieces of work.

I think a lot of people (myself included when I've felt the pressure to) lowball how long things like this take because a) it makes me look smart and b) people could judge of they knew who much time I actually wasted on it.

Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#178

Post by dsaavy »

an_opabinia wrote: post #31

Andrew Gelman designed the 538 model in 2007. Nate Silver authored an adjustment to polls used in that model. Polls have more impact if they are more representative of statewide turnout among demographic things he chose like “black” and “low income.” This is why his predictions were so accurate for Obama’s 2008 and 2012 elections, and likely why they were so inaccurate in 2016. Gelman’s own grad student is the only p…

I think polls being more representative of turnout amongst minorities could help indicate a potential black swan event for the election. If turnout does return to 2008 and 2012 election levels, polls featured in this fivethirtyeight article [1] indicate Trump is performing better amongst black and hispanic voters. Both demographics are seeing a 10-15% swing in support for Trump compared to 2016, which could theoretically cement swing states like Florida, Pennsylvania, and Michigan.

I don't think it's likely but if those polls are indicative of what's actually happening, we're talking about potentially a 2-4 million vote swing in Trump's favor. Here's a link to estimates of voter turnout in 2016 [2].

[1] https://fivethirtyeight.com/features/trump-is-losing-ground-... [2] https://www.pewresearch.org/fact-tank/2017/05/12/black-voter...

Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#179

Post by RivieraKid »

DavidSJ wrote: post #124
RivieraKid wrote: post #84

Earlier quoted context omitted.

> I'm not sure why that kind of interstate correlation should impact predictions? 538 has low positive correlations between states on average, which actually has a big impact, it increases overall uncertainty (and therefore Trump's win probability). Why? If the states are not correlated, you usually end up with a few states going off the rails, like Trump winning Colorado without any nationwide swing.

Other way around: uncorrelated errors tend to cancel each other, correlated errors tend to reinforce each other.

Well Gelman claims the opposite.

Re: Reverse-engineering the problematic tail behavior of Fivethirtyeight forecast

#180

Post by xnyan »

sequoia wrote: post #175

As a US voter I am very frustrated With and tired of this obsession with election forecasting. Is it going to influence whether or not you go out and vote? If not, what is the point of it? What value does something like fivethirtyeight add to our democracy, if any? Is this motivation the same as that of diving deep into baseball stats or Star Wars starship engineering, just like “nerding out” for its own sake? Contra…

>Here’s an idea: everyone go vote for whoever you think the best candidate is regardless of what a stack of polls say.

On the one hand, I think I get your sentiment. On the other, I mean, we are all just solitary individuals floating through this life. Almost all of our important decisions are make at least in part (or more in some cases) dependent on the thoughts and actions of others. That's natural, right? You do otherwise in your life?

If the above is true, it makes total sense why one out of 7 billion plus people would want to understand the choices of others before making theirs.

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