The primary reason why Predictit can't interest anyone in arbitraging is that they don't take "netting" into account when they determine your maximum possible loss. Arbitrage therefore requires you to tie up way to much money, such that it will rarely be a worthwhile investment

At the well-functioning prediction market Intrade, you were required to cover only your maximum possible loss across a mutually exclusive set of contracts (such as a list of people of whom at most one will be elected president). In contrast, PredictIt binds up your funds based on your maximum possible loss at any given contract.

As an example: Suppose buyers are offering to buy one contract on each of 10 possible candidates, at 15 dollars per contract. In other words, there is 50 dollars of free money on the table. On Intrade, you could sell a contract on each, and bind up 100 dollars for a year. This secures you a return of 50% In contrast, on PredictIt you would have to bind up 850 dollars for a year to secure the 50 dollars; which dramatically reduces the effective return to 6%

PredictIt also has a fees structure that discourages arbitrage (by taking cuts on the profits, and calculating the profits on the basis of each individual contract).

I tried to start a discussion about this on the PredictIt forum, but the comment did not make it past moderation. The lack of arbitrage is due to the poorly designed structure of the market. Possibly their hands are tied by the CFTC, I don't think it indicates anything sinister about PredictIt.

This is almost certainly one of those cases where there really is free money lying on the street, but each contract price will have to substantially exceed the interest rate in order to make the investment worth it.

Truthcoin and its cousin Augur deserve a mention, even though neither is actually operational yet. (They're decentralized prediction markets on a blockchain.)

Idea Futures is still running (play money), but is functionally nearly dead and has very low liquidity. Once upon a time it was the best option for play money markets, and quite good.

Fairlay is a half-decent (though centralized) crypto market, though it's structured as a "betting market" and has no way to sell back predictions at a profit or a loss (you can place later predictions to hedge your risk equivalently, but you end up tying up a lot of money). Liquidity is bad.

BitBet runs some sort of weird time-weighted pari-mutuel system that I don't like, and has a lot of complaints about shady operations (eg very, very bad customer support that results in people losing money due to interface mistakes), but they often have actual liquidity.

As far as I can discern, the current state of things is abysmal, but I'm pretty optimistic about Truthcoin (less so about Augur in some ways, but optimistic there too).

Worth noting that PredictIt's odds should give you pause: there's money on the table betting "No" on all the presidential candidates, and I find it concerning that they can't interest anyone in arbitraging that away.

Bridge, the card game. Bidding is the process of two players exchanging information about the cards they hold via the very limited communications channel (bids). The play itself is also used to transfer more information about which cards remain in the hand.

I don't know if that will work as a demonstration of the Aumann's Theorem, though, bridge gets very complicated very fast :-/

example I was thinking:

each player flips 3(? 10) coins of their own. (giving them various possibilities on what they think the whole coin-space looks like) They present their 90%, 99% confidence intervals on there being more than 4 (9) heads. Round 2 repeat. (also make statements based on what they think the state of play is ++ try to get to the answer before the other person. So make statements that can be misleading maybe?)

Not sure how easy it is to tease out that information for a human. maybe a computer could solve it. but not so much a human...

"I flipped 10 coins; My 90% confidence that there are at least 7 of each heads and tails is 90%. 99% confidence is 60%."

confidence for "at least 10 heads and 6 tails" etc.

Based on simple coin flip; other games:

• Several coins;
• scissors paper rock (and then iterated)

I am sure there are more small games that have a similar "known" problem space.

Have several people try to guess the same number, with everyone able to see everyone's guesses and results.

How about some variation on Bulls and Cows?

I'm looking for a good demonstration of Aumann's Agreement Theorem that I could actually conduct between two people competent in Bayesian probability. Presumably this would have a structure where each player performs some randomizing action, then they exchange information in some formal way in rounds, and eventually reach agreement.

A trivial example: each player flips a coin in secret, then they repeatedly exchange their probability estimates for a statement like "both coin flips came up heads". Unfortunately, for that case they both agree from round 2 onwards. Hal Finney has a version that seems to kinda work, but his reasoning at each step looks flawed. (As soon as I try to construct a method for generating the hints, I find that at each step when I update my estimate for my opponent's hint quality, I no longer get a bounded uniform distribution.)

So, what I'd like: a version that (with at least moderate probability) continues for multiple rounds before agreement is reached; where the information communicated is some sort of simple summary of a current estimate, not the information used to get there; where the math at each step is simple enough that the game can be played by humans with pencil and paper at a reasonable speed.

Alternate mechanisms (like players alternate communication instead of communicating current states simultaneously) are also fine.

People who work on drugs to cure horrible diseases don't spend 24/7 in an airtight suit in the lab, dropping samples on the floor because their hands are shaking. They go home and watch football and play card games and go to the kids' school play and stuff.

If they or their kids have the horrible disease? I think they'd react differently.

But being unable to disengage from the Big Problems and live your little ordinary life is not heroism, and it actively gets in the way of solving any of those Big Problems.

Not my Big Problems; they get solved from doing just that.

Find a meditation teacher and spend some time doing that. Practice > theory.

I'm going to have to disagree. I thought you were talking about philosophy when you mentioned "notions of personal identity and continuity, and whether this is an illusion."

The venture could be profitable, yes. Would it generate massive amounts of income? That is also possible. I did not consider a for-profit version of the idea because the project itself was supposed to be charitable in nature. I am considering starting a for-profit branch of this idea, and would be open to hearing other people's ideas and motivations. Is your motivation and other's in getting involved in a for-profit implementation of this idea to earn money?

To elaborate more on profits, the initial implementation of this idea might not be incredibly profitable because we are relying on third party virtual employment services like the aforementioned upwork.com to ensure the initial implementation (this summer!) would be a success and members would be able to find guaranteed work. Directly contracting with people and organizations wanting virtual workers is expected to be a lot more profitable.