Date: Oct 4, 1999 4:29 PM
Author: Steve Schnick
Subject: How to combine the standard deviations of multiple data subsets

If one has several subsets of a given data set, and the mean, count,
and standard deviations for each of these subsets, how can one
calculate the combined standard deviation of the data subsets? i.e.,
if the subsets were lumped together into one set, how does one
calculate this new standard deviation?