I have found many equations which claim to be for weighted standard deviation, yet all of these differ very slightly, and I am confused as to which is the correct one.
I have some data in Excel, and need to use the weighted standard deviation, but want to have a correct equation in order to make a formula.
The image above is the basis I am working with, but I have found other versions in which the (N-1) is missing, the denominator is N-1, or the sum of the weights is multiplied by ((N-1)/N) so that there is a very subtle difference in brackets.
Each one of these options gives widely different results in Excel, hence the confusion.
