How to determine the STDEV of Avg?

[Eric]

Does anyone have any suggestions on how to deterine the STDEV of AVG(10
numbers) for following scores under column A?
I would like to return the STDEV on column B
Does anyone have any suggestions?
Thanks in advance for any suggestions
Eric

61%
99%
100%
72%
50%
71%
47%
57%
78%
73%
79%
95%
68%
69%
48%
45%
42%
44%
57%
62%
40%
41%
42%
46%
35%
32%
33%

 

[Roger Govier]

Hi Eric

=STDEV(A1:A27)

 

[David Biddulph]

How many groups of 10 are you planning to average from your 27 numbers? How
are you going to choose those groups? However you decide to take those
averages, you can then use the list of cells with the averages as the input
to your STDEV formula, but it isn't clear what you are trying to achieve
with the calculation.

 

[Gary''s Student]

With your data in A1 thru A27, the average is:
=AVERAGE(A1:A27)
or
0.58741 (which is about 58%)

The standard deviation is:
=STDEV(A1:A27)
or
0.19833

 

[joeu2004]

Does anyone have any suggestions on how to deterine the
STDEV of AVG(10 numbers) for following scores under column A?

Your question is unclear because of ambiguous use of terminology.

If you mean the standard deviation of the __data__ in column A, I
would use STDEVP(A1:A27) if the data represents the entire population,
or STDEV(A1:A27) if the data represents a sample of a population. But
of course, those are 27 numbers, not "10 numbers".

If, instead, you mean the standard deviation of the averages of a
random sample of 10 of the 27 data -- aka the standard error -- I
would use the following formula:

=stdev(10 numbers) / sqrt(9)

where "10 numbers" is a range that contains 10 of the 27 data, chosen
randomly. One way to accomplish that is to put =RAND() into 27 cells
parallel to A1:A27, then use Data --> Sort to sort the column of
RAND() results and A1:A27 together. Then you can use STDEV(A1:A10) in
place of "stdev(10 numbers)" above.

Finally, if you intend to get N random samples of 10 of the 27 data,
and you truly want to take the standard deviation of the averages of
those N samples, unless you use a macro, I think you would have to put
each of the random samples into N columns (say C1:C10, D110, etc).
That can be done with cut-and-paste-special-value by repeating the
sort procedure described above. Then, if you compute the average of
each column in row 11 (e.g. =AVERAGE(C1:C10) in C11), you could
compute the standard deviation of the averages using, for example,
STDEV(C11:J11) for 8 samples.

HTH.


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