Dear Richard.
The residuals potentially have heterogenous variances
but I have not done the work to match them to the model
or to recognise the heterogeneity.
Hence the 'outlier' calculations just use the information
in the residuals. In normal data, SUM(ABS(RES))/COUNT/0.8
is an alternative calc for the standard deviation. It is an
attempt to use something robust if there actually are extreme values.
So, the possible outliers reprted are just those
records which exceed the criterion and may not be
outliers at all - especially if the residuals have
heterogeneous variances.
Bruce's suggestion of looking at the residuals yourself is a good one.
Arthur
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> From: rkerr1@lush.une.edu.au
> Subject: outliers
> To: asreml@chiswick.anprod.csiro.au
> Date: Fri, 27 Apr 101 11:14:58 +1000 (EST)
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>
> Hello,
>
> I am a bit unclear about the outliers in the .res file. The manual states
> that these are residuals which are more than 3.3 'standard deviations'
> in magnitude. Further on, there is some discussion of these standard
deviations
> in relation to a spatial analysis.
>
> I am not doing a spatial analysis. Is the standard deviation still
> SUM(ABS(RES))/COUNT/0.8 ?
>
> What exactly is this? I am not sure at all how the standard deviation is
> calculated.
>
> regards,
>
> Richard Kerr
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Arthur Gilmour PhD mailto:Arthur.Gilmour@agric.nsw.gov.au
Principal Research Scientist (Biometrics) fax: <61> 2 6391 3899
NSW Agriculture <61> 2 6391 3922
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