STDEV without average

  • Thread starter Thread starter daniel
  • Start date Start date
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daniel

To calculate standard deviation you need to know the average.
How can excel calculate the STDEV of a few numbers without knowing the
average?
Thanks
Daniel
 
What makes you think Excel does not know the average. If you gave me a list
of 10 (small) numbers on a piece of paper I could tell you the maximum. I
might also be able to add them up and divide by 10 without telling you I
have done it!

STDEV is not a simple function. I expect it was written in some version of
C.
best wishes
 
To calculate the standard deviation you need Xi, X and the n. What I'm
asking is how can excel make the stdev calculation without these
numbers? What exactly do I get by marking a couple of numbers and
pressing STDEV?

Thanks
 
daniel said:
To calculate the standard deviation you need Xi, X and the n. What I'm
asking is how can excel make the stdev calculation without these
numbers? What exactly do I get by marking a couple of numbers and
pressing STDEV?
Click to expand...

Excel calculates the average internally. You don't need to explicitly
tell Excel the average, it already has your set of numbers.
 
daniel wrote...
To calculate the standard deviation you need Xi, X and the n. What I'm
asking is how can excel make the stdev calculation without these
numbers? What exactly do I get by marking a couple of numbers and
pressing STDEV?
Click to expand...

By this logic, how does Excel calculate AVERAGE since it requires Xi
and n, but only the Xi are passed to it? Answer: it counts how many
data points are passed to it itself. Similarly, STDEV calculates the
average itself as well as the second moment (uncentered in XL2002 and
prior, centered in XL2003).
 
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