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

Prof Brian Ripley ripley at stats.ox.ac.uk
Thu May 12 18:16:54 CEST 2005

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)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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