Re: a simple(?) probability question...

On Jan 30, 1:23 am, "Joe" <jconcor...@xxxxxxxxxxx> wrote:

[snip]

What I mean by the 50:50 chance for any year is this. For any single
year in the 100
year time span the storm will occur or will not occur in that year.
There are only two possible
outcomes in any one given year and they are equally likely. Would you
agree that means 50:50 chance.

Nonsense.


It does not mean there will be 50 storms in a 100 year span. The
expected outcome for the
100 year span is one storm. Also, there is no reason to expect that
the storm is more likely to occur in
year 75 than in year 10. The Poisson function gives prediction of a
30 or so % chance for a storm within
the first 50 years of a 100 year term. That doesn't make sense to me.
That would say you have a 70 or so %
chance for it in the last half of the century. What natural causes
would make that so?

I'm wondering if one of your misconceptions is that you think the
Poisson process has some sort of built-in knowledge of 100-year cycles
- some sort of "memory" that says, for example, "this is what happened
in the past 50 years, so this is what I need to do in the next 50
years to fulfil the 100-year expectation".

This is not the case. There is no memory. There is no knowledge of
hundred year cycles, or where they begin and end. Time is continuous
and featureless: at every moment there is exactly the same probability
of the event happening, irrespective of what happened in the past or
what is going to happen in the future. Every n-year interval is
probabilistically identical, regardless of where it actually begins
and ends in time (of course, there is a correlation between
overlapping intervals).

With the right parameters the expected (i.e. average) number of events
in any 100 year interval can be made equal to exactly one. This is the
statistical outcome of that stream of constant moment-by-moment
probabilities, but the process doesn't "know" it: it just trundles
along dumbly and blindly.

.

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