@Shary wrote: Hello:   Thank you for replying . Yes, I have more than 4952 clusters. What I want is to calculate the sample size for clusters. I saw in book that you can minimize the variance of the mean and the cost function using Lagrange.   In random sampling? I think you may need to read more carefully what that book was referring to. Lagrange normally refers to building transforms from the data and would more typically be done after a selection, I would think. Not as part of a random sample selection.     ... View more