Re: extra variance component

Dear Alistair,

You wrote
I have just changed to ASReml 2 and am having a small problem with my
animal models - specifically I keep getting an extra "variance" term
reported. I've just run a few simple univariate models and this seems to
only occur if I actually include the variance model. So for example;

y ~ mu !r animal

Gives me Va and a residual variance as expected but,

y ~ mu !r animal

1 1 1

0 0 ID 0.35

ANIMAL 1
ANIMAL 0 ID 0.02

Gives me e.g.

Source Model terms Gamma Component Comp/SE %
C
 Variance 5571 5562 1.00000 3.37476 0.00
0 S
 Residual identity 5571 0.111444 0.376097 39.74
0 U
 ANIMAL Ainverse 10044 0.544778E-02 0.183850E-01 2.79
0 U

The problem being the extra, unexpected "variance" component.I checked
the updated part of the manual but couldn't work out what I'm doing
wrong. Has the coding of the variance model changed or am I just
missing something obvious? Any thoughts would be very welcome.

Alastair

The model is the same as before, or should be, but is not specified
correctly
(the residual variance is implicitly present twice).
What has changed is that ASReml now stops when it detects a singularity in
the Average Information matrix so that the problem can be fixed rather
than
possibly not being noticed as in ASReml 1.

So the correct ways this model can be written are:

y ~ mu !r animal
0 0

or

y ~ mu !r animal

0 0 1

ANIMAL 1
ANIMAL 0 ID 0.02

or

y ~ mu !r animal

1 1 1
0 0 ID 0.35 !S2==1

ANIMAL 1
ANIMAL 0 ID 0.02

or

y ~ mu !r animal

1 1 1
0 0 ID

ANIMAL 1
ANIMAL 0 ID 0.02

Note that the third of these may fit the variance model on the variance
scale rather than on the GAMMA scale which is the default for the other
models.

I trust this clarifies the situation.

ASREML 2 is now available from http://www.VSNi.co.uk

Check out my personal site http://www.cargovale.com.au/

Grace, mercy and peace to you from God our Saviour Jesus Christ

Arthur Gilmour PhD
mailto:Arthur.Gilmour_at_dpi.nsw.gov.au
Principal Research Scientist (Biometrics)
NSW Department of Primary Industries
Orange Agricultural Institute, Forest Rd, ORANGE, 2800, AUSTRALIA

fax: 02 6391 3899; 02 6391 3922 Australia +61
telephone work: 02 6391 3815; home: 02 6364 3288; mobile: 0438 251 426

http://www.dpi.nsw.gov.au/reader/17263
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Leave 18 Dec to 5 Jan
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Received on Sun Sep 19 2006 - 11:18:45 EST