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Re:Kelly Criterion (2007) by soVeryTired on Monday November 19, 2018 @04:47AM (#18485184)
The the main flaw of the kelly criterion (along with a number of other results in investment theory like Markowitz allocation) is that in practice it's extremely difficult to know the distribution of the result you're betting on.

The mean and variance of a prospective investment are not observable. But more to the point, if you try to use some sort of proxy like a sample mean or standard deviation, you'll get inconsistent results over time. We're a long way from the clean, simple, i.i.d world that theorists like to play in.

Re:Kelly Criterion (2007) by downandout on Monday November 19, 2018 @06:18AM (#18485607)
in practice it's extremely difficult to know the distribution of the result you're betting on.

This of course depends on your use case. For example, the Kelly Criterion is a staple of advantage gambling. For most casino games, probability distribution can be easily calculated with absolute accuracy. I'm sure there are other use cases for it where probability distribution is also fairly stable.

Re:Kelly Criterion (2007) by fjsolwmv on Monday November 19, 2018 @07:56AM (#18486051)
Does Kelly work when "ruin" is not such a clear cut permanent barrier? I can be "ruined" today but have more money next payday.
Re:Kelly Criterion (2007) by downandout on Monday November 19, 2018 @08:45AM (#18486321)
This would be less a Kelly issue and more an issue of the bankroll variable you're using. Advantage gamblers generally find the concept of "sessions" meaningless - essentially, one's entire gambling career is just one long session. So if for example you have $1K per week of expendable income that you wish to use for the bankroll, and you're willing to risk that amount for a year, then you'd likely want to approach the Kelly calculation with a $52K bankroll. You would have wild swings within that year, and very short sessions when you lost (because you couldn't play again until your next paycheck), but you would still be betting the correct amount for the total risk you're willing to take.
Re:Kelly Criterion (2007) by pyrex41 on Monday November 19, 2018 @10:21AM (#18486997)
This is also an argument for finding investments that allow you to better define the downside risk of investments. I think that this is why static investments or hedges have such value; they may not change the expected value, they might even reduce it (based on mean estimates), but they reduce / eliminate the estimation error in your downside risk, allowing you a much more certain calculation of leverage.
Re:Kelly Criterion (2007) by aidenn0 on Monday November 19, 2018 @12:33PM (#18488028)
Insurance in general has a reduced expected value while also hedging against downside risk.
Re:Kelly Criterion (2007) by miketery on Monday November 19, 2018 @04:48AM (#18485194)
In such cases what are models that are more effective?
Re:Kelly Criterion (2007) by soVeryTired on Monday November 19, 2018 @05:05AM (#18485268)
I don't know of anything that's guaranteed to be effective out of the box. But as a rule, simpler is better. Any assumptions should be picked apart with a fine-tooth comb and tested for robustness. But in the end, there's not a whole lot that you can do: just cross your fingers and hope.
Re:Kelly Criterion (2007) by iopq on Monday November 19, 2018 @06:56AM (#18485768)
You could probably model something that uses sampled variance less aggressively
Re:Kelly Criterion (2007) by sjg007 on Monday November 19, 2018 @07:41AM (#18485966)
Something bayesian