Standard Deviation do I use 520 (20x26) inputs or avg of each

[sgreene]

We have 520 inputs...20 categories x 26 participants
For the Standard Deviation do we use the average of the 20 categories or the
520 inputs? We used stdevp on the 520 and got 1.1 When we used the stdevp
on the averages of the 20 categories we got .3
Can you help we are not sure which one is correct?

 

[Dave F]

What is the population for which you want to calculate the standard
deviation? If the population is the set of all observations, then it sounds
like your population is the 520 observations.

As for taking the average of categories--I'm not sure what you mean by that.'

Dave

 

[sgreene]

Thank you Dave,
All total we have 520 responses
Each response fits under a certain category..there are 20 categories
We take and total the responses (numeric value) add them up to get a final
average for the column.
When I said that we took the averages I meant that we took the "final
averages" for each category and got the .3 standard deviation
The total population (20x26) standard deviation comes out to be 1.1
I hope this explains it more.
Thank you,
Sharon

 

[Dave F]

Well again I think you need to determine what your population is. Is the
population the average of the categories or is the population the 520
observations?

I don't know why you would take the standard deviation of the former, but
there may be a reason for it.

Dave

 

[bj]

Which one you should use depends on which one you need for your next set of
calculations. You may need both depending.
Both are valid statistics, but have different uses
The issue is not an EXCEL issue. You need to go to a statistician and
describe your needs and he will be able to determine which one you need