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Re: [HACKERS] Perl Standard Deviation function is wrong !

From: Brook Milligan <brook(at)trillium(dot)NMSU(dot)Edu>
To: andreas(dot)zeugswetter(at)telecom(dot)at
Cc: colink(at)latticesemi(dot)com, jason(at)wagner(dot)com, dg(at)illustra(dot)com, hackers(at)postgreSQL(dot)org
Subject: Re: [HACKERS] Perl Standard Deviation function is wrong !
Date: 1998-06-05 15:16:27
Message-ID: 199806051516.JAA18629@trillium.nmsu.edu (view raw or flat)
Thread:
Lists: pgsql-hackers
     >Variance is just square of std. dev, no?

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

I think the difference really has to do with what you are calculating.
If you want the std. dev./var. of the data THEMSELVES, divide by the
count.  If you want an estimate about the properties of the POPULATION
from which the data were sampled, divide by count-1.  People have
needs for both in different circumstances.

Perhaps there needs to be two versions, or a function argument, to
distinguish the two uses, both of which are legitimate.

Cheers,
Brook

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