Predicting randomness

Discussion in 'Trading' started by oddiduro, Nov 3, 2005.

  1. nitro

    nitro

    This game makes no sense.

    It is obvious that at all time, each share's "Fair Value" is $.09 (in theory there is $900 chasing my 100 shares at time Tzero, so if I want everyone's money I have to make sure that I don't sell them for less than about .09 at time Tzero. By symmetry that condition holds for everone else too). Why would anyone bid more than $.09 for shares at time Tzero, and why would anyone offer their shares for less than $.09? In a real stock market, value is almost never based purely on psychology as earnings and dividends and book value eventually enter the equation (as well as things like how much my money can earn in a risk free asset.) How does this game even get started? The only way this game can get started is if someone breaks the symmetry and bids more than .09 or offers their shares for less than .09 for 1 share, at which point FV may change dynamically for those shares, but FV is always apparent - something that is clearly not true in a non-closed system like a real stock market.

    Furthermore, if someone ends up with all the money, why is that considered winnning? What happened to all the shares? Do you mean he ends up with all the money and all the shares? In a real stock market someone may have all my money but I have all the shares which means I can easily convert my shares back to cash assuming a liquid market and a non bankrupt company.

    My guess is you left something out.

    nitro

    PS - the way I would do it would be to set up an options market on those shares witha nice spread and act as a market maker :D

     
    #141     Nov 5, 2005
  2. danoXP

    danoXP

    A Random Walk on Price (even one with a positive bias) can go negative.

    Most markets can only go to zero.

    Many markets cannot go to zero.

    Most market prices cannot be random walks.
     
    #142     Nov 5, 2005
  3. nitro

    nitro

    I am not convinced this argument holds true.

    For example, given that (some) makets tend to rise naturally because of rules that make it hard to sell them, once you take the coordinate transformation into that coordinates system (the "axis" are no longer time/price but functions in some abstract non-commutative space), prices may indeed be locally random.

    What is really interesting is that prices can be locally "random" on that manifold and still have global statistics that have a stable attractor, until something comes and knocks them out of that trajectory.

    nitro
     
    #143     Nov 5, 2005
  4. danoXP

    danoXP

    Fooled by Randomness?

    What "market"? I assume the US equity market? Measured in what way? The DJIA? the SP500? the NASDAQ? none of which existing in its current form 10 years ago? ... even with surviorship bias you are talking about maybe a 100 year time period on the DJIA. You would define an upward bias with 100 data points?

    When the automobile was invented, if you had bought all the auto maker's stocks equally, would you have upward bias today?

    Similarly, when the telephone was invented, and you equally bought all the independant telephone companies (before their consolodation and regulation). Would you have upward bias today?

    Think Railroads.

    Think power companies (the lightbulb).

    Think the computer! (DEC, Data General, Wang, Sperry, Univac, Tandy, IBM, Prime, Sun, Apollo, Metheus, Apple, SGI, Amdahl, etc.). Was there upward bias?

    Now think the Internet. Of the hundreds of IPOs in the late 1990s. Was there upward bias? Did you pick only Yahoo, Amazon and Ebay? If you threw $ at each IPO equally ... would you have upward bias?
     
    #144     Nov 5, 2005
  5. My response is the error in thinking in small numbers and the resulting overconfidence that it brings.

    In other words, is your representative sample large enough? Have you been correct 75% of the time for say 10 years, or mere 10 months.

    Something to consider.
     
    #145     Nov 5, 2005
  6. Uhh, if you are 'betting the farm' then you will certainly blow up some day. You should always hedge your bets and limit your downside.

     
    #146     Nov 5, 2005
  7. see attached
     
    #147     Nov 5, 2005
  8. rols

    rols

    Thanks for that!
     
    #148     Nov 5, 2005
  9. My response would be the error of projecting one's failed attempt to time intraday or short term price movement of a broad stock index to conclude that all price action is random. An index of 500 companies whose daily volume is made up in large part to hedgers and options games would just as well appear to be completely random. Compare that to the stock of a relatively unknown company slowly taking market share from it's competitors and being quietly accumulated by several large funds.

    But the question of randomness aside, you might want to consider why you would ever need to have a sample of any method working for so long as a decade, and why you even have an assumption that such a thing exists in the first place. If a single static condition that produces profits over such a long period of time is the goal of your search, then yes you are probably doomed to fail, because markets in essence are all about changes in perception and expectation. After all, do you really think markets should move dependably because of some chart pattern anyone with access to a data vendor can see?

    Just because something works for a certain period and eventually stops working does not make it random. Just because markets seem to make moves that defy logic does not make it random. Given the right perspective on markets, these results should be expected. To only conceive that markets should do X because of event Y is like sitting at a poker table and just playing from your own hole cards and considering nothing else; you might succeed consistently with the weakest opponents but you'll never last long otherwise. Markets are not predictors or mere reactors to random events, they are constantly changing discounting mechanisms. We as individual traders may not have the capability of knowing "why" price moves until after the fact, but that's no reason to resort to randomness to "disprove" the reason's existence in order to make us feel better about our shortcomings.
     
    #149     Nov 5, 2005
  10. Right.

    To me, the logical extension of the random walk theory is a grander, 'everything is random' theory, which suggests that companies 'slowly taking market share' from their competitors are doing so randomly, that there is no cause and effect operating, and that the efforts of the entrepreneurs whose ideas are successfully realized are actually 'random' events. All achievement then becomes random, and not the result of directed efforts by active agents. I don't have the theoretical chops to describe what I am feeling, but I just keep coming back to this question - how is the movement of the company illiquid described, or the cotton market during a period of blight, random??

    The weather may be random but human responses to it are not.

    And it doesn't do any good to say that there are 'periods' of non-random behaviour but that the overall market is random. Once you admit that there is causality in the markets, every move must be seen in those terms.

    I can't tell you how bizarre this whole idea of non-causality in the markets seems to me.

    This argument seems to me to be akin to the one about religion or pro choice/pro life. People, including me of course, hold their beliefs and there isn't much that can be said that would change anyone's mind. This is so bizarre because an objective analysis disproves the random walk theory so easily :):)
     
    #150     Nov 5, 2005