st: xtsum formulas

[Podest�, Federico <Federico.Podesta@amm.unitn.it>]

Dear all

I have (I think) a simple problem: I would like to know formulas used by the -xtsum- command to obtain the betweem standard deviation and the within standard deviation.
In particular I would like to know Stata code to compute such statistics by hand solving all parts of the formulas step by step.

Thanks a lot in advance for your help!

Federico Podest�

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