You can calculate both the mean of the standard deviations from the sets to find the mean standard deviation. If you have variable set size you can weight the deviations. You can also calculate the mean of all your data points and find a standard deviation for all these points in the usual way.
Then you have to decide which one you want. To do this you have to think about why your data was in sets in the first place, what standard deviation is and what you want to use it for and think about degrees of freedom.
Not a complete answer but hope this helps.
Steve Schnick <firstname.lastname@example.org> wrote in message news://email@example.com... > 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. > >