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AW: [HACKERS] Standard Deviation function.

From: Andreas Zeugswetter <andreas(dot)zeugswetter(at)telecom(dot)at>
To: "'Bruce Momjian'" <maillist(at)candle(dot)pha(dot)pa(dot)us>
Cc: "'hackers(at)postgresql(dot)org'" <hackers(at)postgresql(dot)org>
Subject: AW: [HACKERS] Standard Deviation function.
Date: 1998-06-05 08:07:40
Message-ID: 01BD9069.FC98A570@zeugswettera.user.lan.at (view raw or flat)
Thread:
Lists: pgsql-hackers
>> I had asked you how to calculate this and the variance early last
>> year.  One (I think the variance) was two-pass because of the need
>> for the average, but I thought the StdDev would work with the struct.

>Variance is just square of std. dev, no?

No !   Stdev is divided by count, Variance by (count - 1)

It was some time ago, but I thing there is a running function that 
can be calculated with one pass. I might be able to dig it up somewhere.
I had it in an excel sheet for learning purposes.

Andreas



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