Investor who
wants to beat market must have EDGE and view on how much money to invest on
that stock. i.e optimum amt of money to maximize the geometric mean.
One important
thing I have disclose by my own learnt lesson that “ you are unlikely to
get an edge out of what you see in news/tv.” . The stock market more
effient than the many small investor think. The way to achieve edge is path
shown by Charlie Munger, Multidisciplinary thinking which I had discussed
earlier.
Today we will
discuss about How much to invest (Bet Size) when you have EDGE.
Always Geometric
Mean (GM) less the arithmetic mean (AM) so geometric mean is conservative way
of valuing the risky proposition.
Warren Buffet
repeatedly stressed the importance of patience
as the most important trait investor has to posses in investing , which means
that you should invest only when you have edge and Jhon Kelly
tell how much to bet .
Kelly criterion maximizes the median wealth and The Kelly system leads
to a distribution of wealth (among scenarios or parallel universes) also shuns
the tiniest risk of losing everything, for unlikely contingencies must come to
pass in the long run. The Kelly criterion has, “automatically built in…
air-tight survival motive.”
Kelly formula gives fraction ( f ) bank roll to invest.
f
=Edge/odds where: edge: Amt you will win
odds : profit if you will win
=(P*W-q)/W P= probability of winning , q= 1-p = probability of losing
W=winning amt per Rs invested
Example: In coin tossing on one Rs bet, Heads u get Rs
2, tails you loose. So fraction of your bankroll to bet for maximise GM is (p=1/2,q=1/2,W=2) 25%.
f=( ½*2-1/2)/2=25%
Same can be
applied to buying stocks to maximise your portfolio return.
No other money
management system has a higher geometric mean than the Kelly system does.Another
good feature of the Kelly criterion is that it maximizes the median wealth.
Kelly system
cannot do is engineer luck. It is possible to be unlucky when using the Kelly
system, to end up with less than the median. When you do, you may be worse off
than you would have been with another system.
The
ever-expanding web of possibilities is like that interpretation of quantum
theory where every chance event splits the world into parallel universes. By
the fourth toss, there are 16 distinct parallel universes, corresponding to
every possible sequence of heads and tails
In an infinite
series of serial Kelly bets, the chance of your bankroll ever dipping down to
half its original size is…½. A similar rule holds for any fraction 1/n. The
chance of ever dipping to 1/3 your original bankroll is 1/3. The chance of
being reduced to 1 percent of your bankroll is 1 percent.
The good news is
that the chance of ever being reduced to zero is zero. Because you never go
broke, you can always recover from losses.
The bad news is
that no matter how rich you get, you run the risk of serious dips. The 1/n rule
applies at any stage in the betting.
A fractional
Kelly bet doesn’t sacrifice much return. In case of error, it is less likely to
push the bettor into insane territory.
For true
long-term investors, the Kelly criterion is the boundary between aggressive and
insane risk-taking. Like most boundaries, it is an invisible line