Standard Deviation question
Join Date: Dec 2007
Posts: 1,317
Assume I have a data set where each element has a mean of 30 and a SD of 5.
Take the sum of 10 of these elements. Clearly the mean would be 300. How would I find the SD of this sum?
I do not know the value of each element, only the mean and SD.
Join Date: Aug 2011
Posts: 5,081
If each element is uncorrelated then the variance of their sum is the sum of their variances, so the standard deviation of the sum is √250 ≈ 15.81
For n elements it would be 5√n
If the elements are correlated then you need to know each covariance.
