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Yes, some states had big polling errors, while others like GA and AZ were reasonably accurate. But the model doesn't care if the polls are off in FL by 0.1% or

by awb 6y ago

Yes, some states had big polling errors, while others like GA and AZ were reasonably accurate. But the model doesn't care if the polls are off in FL by 0.1% or 10% because it's a winner take all scenario. So while large polling errors are surprising, they have the same exact impact as a small polling error in a close race, which isn't surprising. But people like to cherry pick and say "how did you get X so wrong?" rather than "how did you get X/10 so right?" In fact, Trump might only end up winning 3 "upsets": FL, NC and ME-2, but they were all under 2% difference in the polls, so no one is shocked to see Trump win there. WI and MI would have been much bigger upsets, but that didn't end up happening and a 20k vote win is as good as a 2M vote win in the EC. The 10% odds come from the path to 270. Here are the 9 states / districts that polled within 2% pre-election (considered toss ups): NE-2, AZ, FL, NC, ME-2, GA, OH, IA, TX. Even if Trump won all of those, he wouldn't get to 270. Using 50/50 odds for all 9 toss ups, Trump only gets a clean sweep 11% of the time. He would then still need another state like PA, WI or MI to get to 270. That's why Silver said that Biden's chances are so high, specifically because Biden could overcome a 2016-level polling error in every toss-up state and still win. In fact we saw 2016-level polling errors in some battleground states, but not all. Another way to view it, is you have a 1/6 (16%) chance of rolling a 1 on a 6-sided die. Even if all 53 states and districts were projected at 84% confidence, and rolling a 1 meant "upset" and rolling 2-6 meant "polls were accurate", you'd end up with 8-9 states resulting in upsets! 84% confidence still means a lot of surprises. Their final FL prediction was only 69% confidence. Also, confidence intervals aren't linear, meaning that a 95% confidence anticipates half as many upsets as a 90% confidence interval. That +5% means -50% upsets, so 69 or 84% confidence is really not as sure a thing as it might sound. So, yes it's worth re-examining why polling was very accurate in AZ & GA but very off in TX & FL (specifically Latino's in Miami). But a 10% chance was not crazy IMO given how easy it was for Biden to overcome even huge polling / vote disparities in multiple states and still win. Again, those who disagree are free to get great odds in the betting markets.

nwienert 6y ago
Bringing in betting markets has nothing to do with the point, but you are right on one thing: if you had bet along with Nate’s odds in a simulation you’d lose money in a Monte Carlo simulator based on current results. The end story is the polls weren’t a reliable measure of the vote. Their predictive ability was low, and even playing by the rules of Nate’s model you have to admit he was off by some 30% at minimum. Nate’s model has the average PA poll at Biden +6 (!!) where the final result looks to be under 1 (and could go either way). It’s simply impossible to argue that was an accurate model.
- awb 6y ago
  > Nate’s model has the average PA poll at Biden +6 (!!) where the final result looks to be under 1 (and could go either way). It’s simply impossible to argue that was an accurate model. 538's PA indicator ended at Biden +4.7%. But the overall 538 model doesn't care if a candidate wins PA by +0.7% or +4.7%. The 538 model is designed to do 1 thing: predict the EC winner. It uses state-wide predictions as indicators, but you can't judge a model based on the performance of a single low-level indicator, you judge it by it's final prediction, which is Biden 90% / Trump 10% to win the EC. But yes, the lower you go in the model the higher variance you'll see: Level 1 -> EC Winner (538's focus -- could end up 100% correct) Level 2 -> State Winners (low variance -- could end up 90-95% correct) Level 3 -> State Polling Averages (moderate variance & could be 75-90% within margin of error) Level 4 -> Individual Polls (high variance & could be 60-80% within margin of error) If you click on any individual state (like PA: https://projects.fivethirtyeight.com/2020-election-forecast/pennsylvania/ https://projects.fivethirtyeight.com/2020-election-forecast/...), you can see the state-wide vote projections. Biden was projected to earn between 49 and 55% of PA's vote with Trump expected to get between 45 and 50%. The final outcome looks certain to fall within those expected ranges. Again, the margin really doesn't matter, just that the idea of Trump getting above 50% and Biden getting below 50% seemed pretty difficult, hence Trump's low (but not impossible) 16% chance of carrying the state. I like the way their "Winding Path to Victory" chart (https://projects.fivethirtyeight.com/2020-election-forecast https://projects.fivethirtyeight.com/2020-election-forecast) explains their model. It's basically saying: "Trump's path to 270 likely goes through PA, NE-2, AZ, FL, NC, ME-2, GA, OH, IA & TX, where he has a fighting chance of winning any of those, but a very low chance at winning all of them." On the flip side, "Biden's path to 270 goes through Wisconsin, Michigan, Nevada and Pennsylvania, where he's likely to win all of them". That seems like a pretty reasonable EC prediction to me. If Silver was promoting the model as being able to accurately predict state vote percentages, I'd agree that it's underwhelming. But when you average all of that variability and uncertainty, you can get a pretty reasonable EC winner prediction IMO, at least better than others I've seen that had Biden closer to 95 or 98% to win the EC, or betting markets that had him as low as 60%.
  - nwienert 6y ago
    If every single range it’s at at or below the lower bound for one candidate and at or just past the upper bound for the other, systematically, that’s the definition of a flawed model. You seem to breeze past every point I make, I suppose there’s no educating the unwilling so I’ll leave this thread. The bell curve was systemically off, the polls were systemically off. They actually missed the bounds in many races entirely. The betting markets were much more accurate. I’ll leave this here: https://mobile.twitter.com/NateSilver538/status/1322877824089378817?s=19 https://mobile.twitter.com/NateSilver538/status/132287782408... About 4pts off on average across them all in the same direction, all past the lower bound.

by awb 6y ago

nwienert 6y ago

Bringing in betting markets has nothing to do with the point, but you are right on one thing: if you had bet along with Nate’s odds in a simulation you’d lose money in a Monte Carlo simulator based on current results. The end story is the polls weren’t a reliable measure of the vote. Their predictive ability was low, and even playing by the rules of Nate’s model you have to admit he was off by some 30% at minimum. Nate’s model has the average PA poll at Biden +6 (!!) where the final result looks to be under 1 (and could go either way). It’s simply impossible to argue that was an accurate model.

awb 6y ago
> Nate’s model has the average PA poll at Biden +6 (!!) where the final result looks to be under 1 (and could go either way). It’s simply impossible to argue that was an accurate model. 538's PA indicator ended at Biden +4.7%. But the overall 538 model doesn't care if a candidate wins PA by +0.7% or +4.7%. The 538 model is designed to do 1 thing: predict the EC winner. It uses state-wide predictions as indicators, but you can't judge a model based on the performance of a single low-level indicator, you judge it by it's final prediction, which is Biden 90% / Trump 10% to win the EC. But yes, the lower you go in the model the higher variance you'll see: Level 1 -> EC Winner (538's focus -- could end up 100% correct) Level 2 -> State Winners (low variance -- could end up 90-95% correct) Level 3 -> State Polling Averages (moderate variance & could be 75-90% within margin of error) Level 4 -> Individual Polls (high variance & could be 60-80% within margin of error) If you click on any individual state (like PA: https://projects.fivethirtyeight.com/2020-election-forecast/pennsylvania/ https://projects.fivethirtyeight.com/2020-election-forecast/...), you can see the state-wide vote projections. Biden was projected to earn between 49 and 55% of PA's vote with Trump expected to get between 45 and 50%. The final outcome looks certain to fall within those expected ranges. Again, the margin really doesn't matter, just that the idea of Trump getting above 50% and Biden getting below 50% seemed pretty difficult, hence Trump's low (but not impossible) 16% chance of carrying the state. I like the way their "Winding Path to Victory" chart (https://projects.fivethirtyeight.com/2020-election-forecast https://projects.fivethirtyeight.com/2020-election-forecast) explains their model. It's basically saying: "Trump's path to 270 likely goes through PA, NE-2, AZ, FL, NC, ME-2, GA, OH, IA & TX, where he has a fighting chance of winning any of those, but a very low chance at winning all of them." On the flip side, "Biden's path to 270 goes through Wisconsin, Michigan, Nevada and Pennsylvania, where he's likely to win all of them". That seems like a pretty reasonable EC prediction to me. If Silver was promoting the model as being able to accurately predict state vote percentages, I'd agree that it's underwhelming. But when you average all of that variability and uncertainty, you can get a pretty reasonable EC winner prediction IMO, at least better than others I've seen that had Biden closer to 95 or 98% to win the EC, or betting markets that had him as low as 60%.
- nwienert 6y ago
  If every single range it’s at at or below the lower bound for one candidate and at or just past the upper bound for the other, systematically, that’s the definition of a flawed model. You seem to breeze past every point I make, I suppose there’s no educating the unwilling so I’ll leave this thread. The bell curve was systemically off, the polls were systemically off. They actually missed the bounds in many races entirely. The betting markets were much more accurate. I’ll leave this here: https://mobile.twitter.com/NateSilver538/status/1322877824089378817?s=19 https://mobile.twitter.com/NateSilver538/status/132287782408... About 4pts off on average across them all in the same direction, all past the lower bound.