[Geysers] Help with student presentation

[Ralph Taylor]

Karen,

The Old Faithful prediction formula was a linear regression formula, derived
by fitting a straight line to the set of duration and subsequent interval
points.  Since the eruptions have become strongly clustered about a "short"
and "long" interval, predictions are made by using the mean long interval
for long duration eruptions and the mean short interval for short duration
eruptions.  We generally use the data for the past month in setting the
prediction.

For Grand we track the intervals for the past month and each week over the
summer look for changes.  In the case of Grand the window is set to include
95% of the intervals.  Generally the mean (average) interval is the center
of the window, but the prediction interval is also adjusted so the short end
of the window includes all of the observed intervals on the principle that
people would rather wait for an eruption than miss the eruption because the
prediction was too long.

At present the two geysers that show the strongest correlation between
duration and the subsequent interval are Grotto and Spouter.

Ralph Taylor

-----Original Message-----
From: geysers-bounces at wwc.edu [mailto:geysers-bounces at wwc.edu] On Behalf Of
Karen Webb
Sent: Wednesday, May 25, 2005 17:21
To: geyser observation reports
Subject: [Geysers] Help with student presentation


 From Karen Webb
Hi gang:
    My little boy is trying to put together a presentation on how 
geysers are predicted.  My recollection is that Marler actually 
developed a formula from which the current predictive values for OF 
arose but all I've been able to find is several versions of the table 
that says "if eruption is X minutes long, predict next eruption in Y 
minutes."  Can anyone help us out with the actual math that gave rise to 
this?  Also, for the bigger geysers like Grand with longer windows, is 
the predictive interval based on a certain number of previous eruptions 
(like do they get the interval from the average of Z number of previous 
eruptions, or does it take a certain number of eruptions with a shorter 
or longer interval to prompt the VC to change this interval)?
    Thanks for any info or resources anybody has.
Karen

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