Henry
Posts:
1,089
Registered:
12/6/04


Re: How to combine the standard deviations of multiple data subsets
Posted:
Oct 4, 1999 5:35 PM


On Mon, 4 Oct 1999 14:29:17 0600, "Steve Schnick" <sschnick@yahoo.com> wrote: >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?
Some clues: 1. You need to calculate the new mean. (easy) 2. You should work with variances not standard deviations 3. If a set {Xi} i=1 to n has mean M then sumof (Xik)^2 / n = (kM)^2 + sumof (XiM)^2 / n Ask again if this is not enough

