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Topic: How to combine the standard deviations of multiple data subsets
Replies: 6   Last Post: Nov 23, 2012 1:26 PM

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Jerry Dallal

Posts: 48
Registered: 12/18/04
Re: How to combine the standard deviations of multiple data subsets
Posted: Oct 4, 1999 11:06 PM
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"Steve Schnick" <sschnick@yahoo.com> 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.





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