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Re: HYB: Rolling the Dice


From: "Mike Sutton" <suttons@lightspeed.net>

You guys are scaring me, just make the crosses and have fun!  :-))
Mike
-----Original Message-----



>
>The problem arises if we assume that the "probability of any individual
>seedling failing to meet the criteria is .999" -- because we simply don't
>have the data to support it.   That's why I didn't approach the question in
>terms of statistical probabilities.  All we have is a hybridizers' Rule of
>Thumb -- we're dealing with anecdotal perceptions reported by
>non-statisticians and, to the practicing hybridizer, the 1 in 1,000 figure
>is an instinctive "average".  Actually one of many estimates, depending on
>who is expressing an opinion.
>
>Look at it this way -- if there's one "success" per thousand seedlings then
>for every case in which successes are separated by less than 1000 there's a
>matching case in which successes are separated by more than 1000.   If you
>grow 1000 seedlings, you have a 50/50 chance of success.  If you grow 2000,
>you can expect one good seedling and a 50/50 chance of a second one.   And
>so on, per thousand seedlings.  Simple.  Intuitive.  And completely
>ungrounded in statistics.
>
>The statistical model, OTOH, isn't simple at all.   To those of you who are
>mathematically inclined, I suggest setting up a spreadsheet for the model
>and graphing the distribution.  Most enlightening.  In summary, it shows
>that not only will some successes be separated by considerably less than
>1000 and some by many more -- but also that the probability only
>asymptotically approaches certainty.  The good news is that, as Gerry
>demonstrated, the 50/50 point is skewed in our favor.  The bad news is that
>in this model it would take around 5000 seedlings to reach the 99% chance
>of success.
>
>So how can we reconcile the two?
>
>First, we note that hybridizers avoid exploring the outer limits of the
>statistical model.  We learn to capitalize on success and cut our losses
>when confronted with a string of failures.   When we are fortunate enough
>to achieve early success, we don't feel compelled to raise the number of
>seedlings needed to round out the lot. In short, we do everything we can to
>influence the odds in our favor.  I believe these practices have led us to
>an excessively optimistic estimate of the overall probability of success
>for any one seedling.   If the statistical model used .9995 as the
>probability of failure, the 50/50 point would be  nearer to 1000 seedlings
>and I believe this would more accurately depict empirical observations.
>
>But even that is a guesstimate.  We're rolling the dice.  The important
>thing is to make the crosses, grow the seedlings and have fun!
>
>Sharon McAllister
>73372.1745@compuserve.com
>
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