| 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 |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| 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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