Re: overall mean and predictions
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: overall mean and predictions

> Dear ASREMLers,
> 	Can someone please throw some light on the following ASREML
> prediction:
> I have a model predicting variety means using code:
> yield ~ mu c(Varname) c(tos) c(Year) c(Newzone),
> !r TrialID
> 1 1 0 !WT=nrep
> 0 0 0
> predict Varname
>  The predicted variety means are all exactly 62 kgs lower than those from
>  However, the raw mean is 2347 (which I presume GENSTAT adjusts to,
>  BUT ASREML estimates mu=2421
>  So, strangely, the ASREML overall mean is HIGHER???
>  than GENSTAT.
>           Peter Clarke
> --

Dear Peter,

Simple things first:  Genstat does not allow you to use
'Sum to Zero' Constaints. It uses 'Corner point' constraints.
It predicts the 4way table Varname x tos x Year x Newzone
and then averages over the cells to produce the Varname table.
Is the 4 way table complete?  Genstat has various options for forming means.
when the table is not complete.

ASREML does an equivalent thing but may get different results if
there are holes in the 4way table.

You have used a weighted analysis so this could explain the difference
between the raw mean and mu.

The fixed difference of 62 suggests a difference in the base for
calculation.  The mean of the Varname values from ASREML under
your model should be 2421.  If not, then it suggests that
the other factors are not being averaged over.

I would need to see the Genstat output and the ASREML output to 
comment further.


> Asreml mailinglist archive:

Arthur Gilmour PhD        
Principal Research Scientist (Biometrics)            fax: <61> 2 6391 3899
NSW Agriculture                                           <61> 2 6391 3922
Orange Agricultural Institute             telephone work: <61> 2 6391 3815
Forest Rd, ORANGE, 2800, AUSTRALIA                  home: <61> 2 6362 0046
                                                   Cargo: <61> 2 6364 3288
Until July 2001, I will be mainly building a house at Cargo.

ASREML is still free by anonymous ftp from pub/aar on
    or point your web browser at 

To join the asreml discussion list, send the message  

To send messages to the list,

Asreml list archive:

                        <> <> <> <> <> <> <>
"Blessed are the peacemakers,
        for they shall be called sons of God"   Jesus; Matthew 5:9



Asreml mailinglist archive: