News for hackers. Stuff that matters.
Re:What is ergodicity? (2016) by uniformlyrandom on Wednesday June 26, 2019 @12:39PM (#20286640)
Interestingly, ergodicity has two meanings (https://www.merriam-webster.com/dictionary/ergodic):

1. of or relating to a process in which every sequence or sizable sample is equally representative of the whole (as in regard to a statistical parameter)

2. involving or relating to the probability that any state will recur especially : having zero probability that any state will never recur

Nassim Taleb mostly uses ergodicity in the second meaning, while the article concentrates on the first. I find it utterly confusing.

Re:What is ergodicity? (2016) by vbuwivbiu on Wednesday June 26, 2019 @01:25PM (#20287085)
Taleb uses his own definition of ergodicity which he's yet to state
Re:What is ergodicity? (2016) by dxbydt on Wednesday June 26, 2019 @04:03PM (#20288581)
I’m curious why you would think that.

afaik, Taleb has repeatedly & explicitly stated “no probability without ergodicity”, which is pretty much a frequentist mantra. The problem with non-statisticians like Nate Silvers (who holds a BS in Econ, as opposed to Taleb who earned his PhD in Statistics), is that they traffic in electoral polls involving human subjects which are anything but ergodicity. Yet, they brazenly attribute probability models to their conclusions. That has severe definitional issues, which is what Taleb objects to.

As to the gatekeeping issues, my mom buys eggs for $3 and groceries for $7. 3+7=10, so she hands over a $10 bill. Wait a minute, does that mean my mom is a mathematician, because she has engaged in arithmetic, which is math ? That’s the issue here. Silvers can simply post how many people want to vote which way & leave it at that. It’s just an opinion poll. Instead he engages in an elaborate charade where he takes polls of polls, ensemble averages, then says this is what is most likely, then on election day when most likely becomes least likely, he washes his hands off. Thats just clearcut fraud. All Taleb is saying is that you simply don’t have ergodicity here so you don’t have a probability. You just have a [0..1] fraction that doesn’t mean much because it doesn’t converge to a limit as information approaches infinity. So if you had skin in the game and purchased an option based on the projected outcome you would lose big time.

Re:What is ergodicity? (2016) by yellowstuff on Wednesday June 26, 2019 @05:21PM (#20289323)
I don't understand your (or Taleb's) point. If you insist on "no probability without ergodicity" then you can't put a probability on stock price movement, or any election or sporting event. But people put probabilities on those all the time. If that breaks the assumptions of frequentist models then it's the frequentists who are wrong about what people mean when they use probabilities.

I agree with the idea that Nate Silver is an entertainer, and if he were a bookie he'd need to be more precise about the odds he places on things and his range of uncertainty. But to me that doesn't suggest that Silver shouldn't speak in terms of probability at all. For a journalist (a big caveat) he's remarkable for being rigorous, open about his level of certainty, and willing to admit to mistakes.

Re:What is ergodicity? (2016) by patrick5415 on Wednesday June 26, 2019 @07:51PM (#20290504)
I disagree that statisticians should adjust their definitions to fit common usage.

I can put any probably on anything I want. That doesn’t imply those numbers mean anything usefu or that what I’m doing is backed by any established theory.

Re:What is ergodicity? (2016) by kgwgk on Thursday June 27, 2019 @02:11AM (#20292121)
There are established theories of probability that have nothing to do with ergodicity. See for example:

Laplace - Théorie analytique des probabilités - 1812

Keynes - A Treatise on Probability - 1921

Jeffreys - Theory of Probability - 1939

Savage - The Foundations of Statistics - 1954

de Finetti - Teoria delle Probabilità - 1970

Re:What is ergodicity? (2016) by vladTheInhaler on Thursday June 27, 2019 @03:42PM (#20297863)
I hardly think it's fair to say that Nate Silver isn't interested in accountability for his predictions. The site recently finished a retrospective that tries to address this issue:

https://projects.fivethirtyeight.com/checking-our-work/

Probability theory, whether frequentist or otherwise, is "just" math. Identifying that mathematical structure with real-world events is always going to involve a judgment call. So if your framework requires assumptions that don't hold in the real world, then maybe it's not the appropriate framework to use. Because clearly people are making decisions based on numbers between 0 and 1, and they're not generally losing big time.

Re:What is ergodicity? (2016) by kgwgk on Wednesday June 26, 2019 @04:12PM (#20288646)
> So if you had skin in the game and purchased an option based on the projected outcome you would lose big time.

Would you lose at any odds? Then the probability is zero.

Would you (expect to) lose at some odds and win if the odds offered were different? Then the probability is somewhere in between.

Re:What is ergodicity? (2016) by kgwgk on Wednesday June 26, 2019 @04:08PM (#20288617)
> as opposed to Taleb who earned his PhD in Statistics

Wrong.

Re:What is ergodicity? (2016) by gowld on Wednesday June 26, 2019 @05:04PM (#20289172)
Management Science / Nassim Taleb - 1998 : The Microstructure of Dynamic Hedging

https://helyettegeman.com/phd-students/

Not so different from economics.

Re:What is ergodicity? (2016) by vbuwivbiu on Wednesday June 26, 2019 @05:34PM (#20289440)
your reply made me question myself so I got Skin in the Game off the shelf and whadddayknow he _does_ give a definition:

"Perfect ergodicity means that each one of us, should he live forever, would spend a proportion of the time in the economic conditions of the entire cross-section[of the U.S. population]: out of, say, a century, an average of sixty years in the lower middle class, twenty years in the blue-collar class, and perhaps one single year in the one percent"

Re:What is ergodicity? (2016) by pcstl on Wednesday June 26, 2019 @01:01PM (#20286863)
Honest question: Aren't both equivalent? If the process will eventually traverse its entire state space, you should be able to infer the behavior of the process across all time from a finite (sufficiently large) sample of the process's behavior.
Re:What is ergodicity? (2016) by AstralStorm on Wednesday June 26, 2019 @01:03PM (#20286879)
Second version is much more loose, e.g. most semi-stationary processes fit the bill.

In fact article makes a mistake by requiring stationary nature from ergodic process. You can have an ergodic process of the first kind where ML expectation is equal to the value of the process function, which nonetheless is not stationary in absolute sense. (Because definite integral does not match indefinite.) Just perfectly predictable and having the indefinite integral identical to integral over space state. Which implies strictly bounded but not exactly stationary in any defined term.

Likewise you can prove an equivalence class of the process to be identical to another known ergodic process without actually calculating such difficult to obtain complete integrals.

And ergodicity is not required for representative sampling either, just definite error bounds on predictive (statistical) power or likelihood estimates. Which can be estimated or directly calculated for many kinds of processes accurately. It is only required for certainty.

Re:What is ergodicity? (2016) by Simon_says on Wednesday June 26, 2019 @08:44PM (#20290790)
Yes, that's the content of the Birkhoff Ergodic Theorem.
Re:What is ergodicity? (2016) by edna314 on Wednesday June 26, 2019 @04:49PM (#20289007)
Naively I would have thought that there is another definition which goes along the lines that a process is ergodic if it looses memory of its starting conditions. But, maybe I’m mixing up things here.
Re:What is ergodicity? (2016) by gowld on Wednesday June 26, 2019 @05:00PM (#20289124)
That's essentially equivalent except in pathological synthetic cases, as time goes to infinity. Since any sample is representative of the whole, samples that don't include the intial conditions are as representative of the whole as samples that do include the initial conditions.
Re:What is ergodicity? (2016) by hgibbs on Wednesday June 26, 2019 @07:56PM (#20290535)
Well, trivially, a dynamical system with that switches between two states is ergodic. We always know what the past state of the system was given the present.

No, ergodicity is more about visiting the each part of the phase space with some positive frequency i.e. on a long trajectory you see everything that can happen, and not too infrequently.

Re:What is ergodicity? (2016) by Retra on Wednesday June 26, 2019 @01:10PM (#20286955)
The dictionary is not a reliable place to look up technical terms. (Actually, it's not a reliable place to look up most anything.)
Re:What is ergodicity? (2016) by uniformlyrandom on Wednesday June 26, 2019 @01:57PM (#20287435)
Are you contesting either of the meanings?
Re:What is ergodicity? (2016) by Retra on Wednesday June 26, 2019 @02:37PM (#20287854)
No, I'm questioning the validity of answering the title question by consulting a dictionary. That's not how one should go about answering technical questions, even if we find it works sometimes. (The proper way to address the question would also allow you to recognize when a dictionary was wrong.)

Dictionaries don't actually tell you what a word means, they give examples of what it may mean from common usage.