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Standard Deviation in Excel

Posted on 2011-09-21
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I don't understand why the value of cell B9 is not equal the value in C8 in the attached spreadsheet. I think they both should be 3.741657.
standardDeviation.xlsx
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Question by:allelopath
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7 Comments
 
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Expert Comment

by:sdstuber
ID: 36574974
they are two different functions

B9 = stddevp(B2:B7)  deviation over entire population N
C8=B10 = stddev(B2:B7) deviation over "almost" entire population N-1

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by:allelopath
ID: 36575005
Yes, but cell C8 is over the entire population, hence I would expect it to be the same as B9, which is also over the entire population.
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Expert Comment

by:sdstuber
ID: 36575023
VAR is also non-biased   i.e.  N-1  (not the entire population)


stddev = sqrt(var)  because both are non biased

stddevp <> sqrt(var)  because stddevp is biased
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sdstuber earned 2000 total points
ID: 36575046
if you want biased variance over the entire population  use VARP  instead of VAR

stddevp = sqrt(varp)
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Author Comment

by:allelopath
ID: 36575053
Oh. Is there VAR for N? I don't see a VARP function.
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Author Comment

by:allelopath
ID: 36575055
oh yes I do ...
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LVL 93

Expert Comment

by:Patrick Matthews
ID: 36581075
allelopath,

Your entire population has 7 members?  Really?

Sarcasm aside, you will nearly always want the sample stdev and sample variance; in actual practice, you will almost never have statistics for the entire population, and once your sample gets to a sufficient size, the difference between the sample and population versions of stdev and variance rapidly approaches zero.

Patrick
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