R help - May 2005 - correlogram in spatial producing values outside [-1,1]

Dear all,

I'm using the correlogram function in the spatial library to calculate
spatial correlograms of radar data.  However, I'm finding that the
resulting values are often outside the range [-1,1], usually only at
larger distances of separation.

I'm not sure whether to be overly concerned about this, or dismiss it as
some artefact of the data.  Has anyone had similar experiences?  Or know
why this might be happening?

Thanks

Kechi

It can happen.  The covariance is produced from a set of pairs, and the 
variances from all the points.  It usually indicates that too fine a 
binning has been used or that there is a trend in the data which has not 
been removed.

On Thu, 12 May 2005, Kechi Nzerem wrote:
> I'm using the correlogram function in the spatial library to calculate
> spatial correlograms of radar data.  However, I'm finding that the
> resulting values are often outside the range [-1,1], usually only at
> larger distances of separation.
>
> I'm not sure whether to be overly concerned about this, or dismiss it
as
> some artefact of the data.  Has anyone had similar experiences?  Or know
> why this might be happening?
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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