Quote from nitro:
I am not making an assertion as to whether people act in herds or not, and whether you could gain information from noticing that they do. That was my whole point about asking the "wrong" question: it doesn't matter to many traders that are hugely profitable. In the hope of being more clear, I am making two statements:
1) Many if not most derivatives traders assume that the underlying follows a [Geometric] Brownian Motion, or said another way that the underlying is a random variable like a coin flip. Whether that is the truth or not is a philosophical question to derivatives traders. The way they make markets or compute theoretical prices completely ignores this philosophical question because the simplification of assuming a random variable and ignoring the philosophical question doesn't affect their profitability.
2) I stated that the question of trying to predict markets confused people into followig the wrong path to trading profitability. I tried to give an analogy by showing how you can make money playing games where the outcome of the event is random and therefore unpredictable by definition. While I do not claim that markets are coin tossing games, the insight gained from reducing the complexities of markets to simple games like these should not be underestimated. In fact, if you understand the mathematics of coin flips and expentancies etc, it is amazing how close you get to the way options prices are derived mathematically.
I had to read this a couple of times to understand what you say I am saying, but I think you got it. I am saying that an option's price does not predict where the underlying goes. It says that given a volatility expectation for that option, I can compute it's fair price by plugging that value along with other less complex parameters into the Black Scholes model. The BS model then outputs the theoretical price. This theoretical price plays the same role as the 50:50 probability that we realize is true for a coin flip. It is the average price when all possible paths are computed and weighted according to probabilities. Same with the coin flip.
We then make a market around that theo price, which is the edge we demand for making a market. If you fill where we make a market, it is like the coin toss game where we demand 60% if we win and we pay out 40% if we lose. Of course, on any one realization of this game, it may be 80:20 or 90:10 or whatever, but over many many trials and many many positions, that or somethig like it is our expectancy. Notice there is no prediction of the underlying whatsoever, and in fact we have no idea which trades will lose or win. Prediction is replaced by computation of fair price, and our edge is the spread we make around fair price, which we demand for taking the risk and providing liquidity.
Nearly 100% of options market making firms do exactly this. It is hugely profitable and has been for decades.
nitro
Nitro,
Thanks for sharing your knowledge. It is post like this with high content value that makes people keep coming to ET.
A question pops up my mind after reading your post - If almost all option MM use such model then to what point would profit be arbitraged out? It seems to me if competition get really bad it would all boil down to execution speed or maybe customer order flows for MM/Broker firms like IB. Of course unless someone come up with a better model and could tighten up the spread further and assume higher risk without blowing up. But then the other guy would come up with still better models and faster executions. Would this ever end? Maybe in the end it's all about having customer orders and no one can make money without having a brokerage operation sitting on top of MM operation?
Is that so? Or maybe the market is just so inefficient?
) So I guess it's more a matter of directional bias with better odds, as per nitro's 60/40 coin toss analogy. But as the competition intensifies with other such sophisticated players, as you suggested, perhaps the hypothetical 60/40 begins to move closer to 51/49. Of course, at this point I'll believe anything.