"Steve Schnick" <firstname.lastname@example.org> writes: > 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? > > Thanks. >
The mean and SD of the combined sample are determined by the individual means, SDs, and sample sizes. The individual data values are ancillary. I let SAS create an arbitrary dataset with the requisite means, SDs, and sample sizes. Then I let it calculate the mean and SD for the combined data set.