That clarifies things, but correct me on a couple of points: my
understanding is that a higher SD predicts a greater probablity
that the
results will fall within the range of averages, i.e. a SD or 1 is
roughty
66% while a SD or 2 is a virtual certainty (the 95% that you
mention).
Please correct me if that is not right.
What the 66% and 95% numbers that you quote refer to are the
probabilities that the end result of a fixed series of trials (eg
video poker hands) will end up within 1 standard deviation of the
mean of the results of those trials (66%) or 2 standard deviations
(95%). If we take a game with a theoretical mean rate of return of
100% and the standard deviation of that return after 1000 trials is
10%, then 95% of the players playing that game, will, after having
completed 1000 trials have between 80% (2 SD below the mean) and 120%
(2 SD above the mean) of the money they had gambled (this is a highly
theoretical example!!).
Also, assuming a large number of trials, you seem to be saying that
while
the "volitility" effects short term outcomes, the SD goes up as
samples
increase. At the same time you say that as samples increase the SD
goes
down. I'm a little confused.
As the number of trials increases so the fit of the data to a normal
distribution improves. The standard deviation of a bigger dataset
will, therefore, be smaller because the observed data fits better to
the expected data ie the outcome is more predictable. Thus for very
large data sets (eg millions of poker hands) the standard deviation
will be much smaller than for small data sets (eg 1000 poker hands).
95% of the results will still end up within 2SDs of the mean, but the
extent of that spread will be much smaller. Using the same game
example as above, perhaps the standard deviation after 1million hands
is 1%(rather than the 10% for 1000 hands). Thus, after 1 million
hands of play, 95% of the time you would end up with between 98% and
102% of the money you had gambled.
Hope that helps,
CPC
> Standard deviation is the root mean square of deviations from the
> mean for a given frequency distribution, and its 'size' will vary
> depending on the number of observations in that distribution. In
> general, the larger the N the smaller the SD. For a normally
> distributed population, 95% of the actual results will fall within
> 2SDs of the mean, but in probibalistic games of chance like video
> poker with highly variable outcomes, this SD is likely to be quite
> large, especially if only a small number of trials are conducted
> (that's why you can win and lose big in the so-called short-
term).In
> terms of 'percent return', I would suspect that all VP games have
SDs
···
--- In vpFREE@yahoogroups.com, "Lawrence Boxer" <ljboxer@e...> wrote:
> much greater than 1% unless very large numbers of trials are
> conducted.