Googling for sphericity gives wikipedia as a first link which says:
Sphericity is a measure of how spherical (round) an object is.

The second hit gives the connection with statistics, in particular  
ANOVA,
http://www.linguistics.ucla.edu/faciliti/facilities/statistics/spher.htm

hth, Ingmar

On Sep 12, 2007, at 5:13 PM, <darteta001@ikasle.ehu.es>  
<darteta001@ikasle.ehu.es> wrote:

> Dear list, first apologies for this is not strictly an R question but
> a theoretical one.
>
> I have read that use of k-means clustering assumes sphericity of data
> distribution. Can anyone explain me what this means? My statistical
> background is too poor. Is it another kind of distribution, like
> gaussian or binomial? What does it happen if the distribution is not
> spherical? Could you give me an example or a link to information about
> this?
>
> Thanks for your help
>
> David
>
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> and provide commented, minimal, self-contained, reproducible code.


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