How is StdDev calculated?
 

The StdDev gave number much smaller than the squre root of sum of square of
deviation from the mean. How is it calculated?

How is StdDev calculated?
 

Type "stdev" in Excel HELP
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--
Kind regards,

Niek Otten
Microsoft MVP - Excel

"xyw" wrote in message ...
| The StdDev gave number much smaller than the squre root of sum of square of
| deviation from the mean. How is it calculated?

How is StdDev calculated?
 

=STDEV(data) should be =SQRT(DEVSQ(data)/(COUNT(data)-1) which is supposed to
be less than DEVSQ(data) by a factor of 1/SQRT(COUNT(data)-1).

If you mis-stated the situation, and STDEV(data) is instead less than
SQRT(DEVSQ(data)/(COUNT(data)-1), then I will guess that you are using Excel
XP (2002) or older, and your data has a small CV (coefficient of variation,
also known as RSD -- relative standard deviation). Older versions of Excel
used a mathematically correct, but numerically unstable algorithm that could
give numerically incorrect results with a small CV or a very large n.

It is had to be more specific without more information about your particular
case.

Jerry

"xyw" wrote:

The StdDev gave number much smaller than the squre root of sum of square of
deviation from the mean. How is it calculated?