Posted by jonbecker 1/19/2026
Could you use inefficient markets as a predictor of great volumes of insider trading?
dataset: 72.1m trades and $18.26b volume on kalshi (2021-2025)
core findings:
longshot bias: well documented longshot bias is present on kalshi. low probability contracts are systematically overpriced. contracts trading at 5 cents only win 4.18% of the time.
wealth transfer: liquidity takers lose money (-1.12% excess return) while liquidity makers earn it (+1.12%).
optimism tax: the losses are driven by a preference for "yes" outcomes. buying "yes" at 1 cent has a -41% expected value. buying "no" at 1 cent has a +23% expected value.
category variation: finance markets are efficient (0.17% maker-taker gap) while high-engagement categories like media and world events are inefficient (>7% gap).
mechanism: makers do not win by out-forecasting takers. they win by passively selling "yes" contracts to optimistic bettors
This is interesting and makes a statement about positive or negative orientation in human psychology. Also, couldn’t the bets just be worded in the double negative instead of the affirmative to influence the optimism bet?
> Yet on Kalshi, a CFTC-regulated prediction market, traders have wagered vast sums on longshot contracts with historical returns as low as 43 cents on the dollar.
On prediction markets traders can bet both sides. E.g. on Polymarket I can currently bet that Greenland will be acquired by USA before 2027 and get 4:1 odds: or I can bet that this doesn't happen, and give 4:1 odds. If these odds are off, doesn't this mean that one side gets a bad return on investment, however the other side gets an equally good return?
On balance the average return on investment by traders should just be 100 cents minus the margin of the prediction market, which tends to be only a few percent.
In fact traders have to be there for both sides. The article means approximately that on 1c bets on unlikely things the people betting 1c to get a dollar if it happens do worse than those betting 99c to make a dollar if it doesn't happen.
I'm not sure that means betting 99c to make a dollar is a great business though - your money is tied up, often the volume is low so if you can only bet say $99 to win $100 it may not be worth the hassle to make $1, and you are vulnerable to the bettors knowing something you don't - maybe the unlikely event isn't really that unlikely but you don't know.
In the "The Mechanism of Extraction" section, how is that image made? It is nicely laid out, and has a nice "hand-drawn" feel. This is a good format for many technical drawings, but I have not found any tools that could create this.
In prediction markets if the markets are fully efficiently priced, in the absence of transaction costs you WILL get 100% back in the long run.
Slots are also unskilled games, prediction markets clearly some participants have a clear market edge, thus not efficiently priced.
> Takers pay a structural premium for affirmative "YES" outcomes while Makers capture an "Optimism Tax" simply by selling into this biased flow.
It's still operating like a casino in that there's a "house edge" that comes from taking bets. Unlike a casino, there is nothing stopping the average person from market making, which is why it doesn't make sense this structural inequality exists.
This is basically equivalent to the observation that, in a perfectly efficient market, no entity can ever make a profit.
And yet, in the real world, entities make profits all the time. In fact, they make wild, unimaginable, world-changing, history-altering profits. This is a tacit admission that our markets aren't even remotely efficient, and that includes predictions markets. Efficient, rational markets are the exception, not the rule.
In a perfectly efficient market all entries can make the same profit on a given investment at the same level of risk and time horizon. There’s nothing inefficient about a market having a risk premium etc.
Instead in an efficient market everyone is already occupied making X ROI and gives as much up by entering a new market as they gain.
Put another way, if you already own a sock with 10% ROI, you can sell it and buy a sock with 10% ROI but the transaction is pointless so it doesn’t occur.
> An efficient market also assumes perfect information, which includes information of future events, so talking about risk/uncertainty is already out of the question.
Perfect information means something different here. In Chess both players have perfect information of the game state, they don’t know the future. Poker has randomness and imperfect information but there’s other games with randomness and perfect information.
If people knew more about economics than just whatever is being parroted as 'economics' in mainstream media they would know that there's a variety of types of markets that happen in the real world and none of them are the abstraction of a free market that allows econ 201 students to compare what happens when you introduce trade between a country that produces 4 apples for 3$ each and a country that produces 5 oranges for 4$ each.
If the odds in some financial products are worse than gambling while everyone can access gambling, then people should stop making a distinction under the guise of protecting investors
it just drives investors to actual gambling because they cant get the exposure they were already looking for
This argument gets trotted out by Wall Street every decade or so, usually under the guise of "democratising" some piece of finance. It's almost always bunk.
Most investment capital is looking for safe returns. It's not competing with gambling. Even within the high-risk end of finance, the game is in turning that high risk into above-market but predictable returns through portfolio mechanics. (Fuckups aside, you can't generally portfolio mechanic your way out of the negative expectated value of a lottery ticket.)
More simply: the notion that we need to increase risk and profitiabilty for intermediaries in investments to keep people from gamblig is a false economy. Gamblers are seeking a different thrill from what financial markets are designed to provide. To the degree we have a problem, it's in letting our markets look more like casinos.
> exposure they were already looking for
Broadly speaking, if you want exposure to the economy you're investing. If you want exposure to a number that goes up, you're gambling. This is an overly-simplistic delineation. But it works for first-order estimates.
I'd almost agree if the volume on $SPY zero day options wasn't so immense.
Which isn't even tied to the spot price of VIX on a daily basis.
So buying VIX as a hedge against black swan events (or Donald Trump's stupidity) is a losing trade, which is wild to me.
The states regulate gambling and the feds only protect the state's rackets by restricting online gambling, and the feds regulate financial markets that are not considered gambling, we get it, its two different governments that don't see the silly user experience they've created and are both very passionate about what they do. The people regulating the financial markets think they are doing a noble good by protecting people from losing their money, and now, fast forward to the present, neither are the regulators of sports betting
I didn't write this about sports gambling or event markets and I don't care about that particular subset. There are many many many markets and financial products either accessible or not, in this paradigm
The user experience is stupid when the dumbest trades are still available after the investor has been protected
The capital wants to move so let it move
The regulators should continue mandating transparency and keeping markets operating predictably, but they need to get out the way of approval or denials of financial products or access to them, because its redundant and silly