Re: MVINCLUDE

Dear Anne,

> I am curious about the use of the MVINCLUDE option in ASReml, especially
in univariate analyses, and would like to clarify when/why it can be
helpful.
> My understanding is that it can be useful for multivariate analyses when
the design matrix has a missing value, in which case it is set to zero,
which can only work for covariates, which have previously been
mean-centered? Is that correct?
** If the covariate value is missing, you must either ignore nthe data
record, or impute some value to replace the missing value.
The MVINCLUDE qualifier imputes a zero. If the data is centred, this is
reasonable. You might of course want to impute a value
other than the simple mean which could be done using the !NA
transformation, or by 'CENTERING' to the required value.

> If applied to a simple model with one categorical fixed effect (e.g.
sex) and one random effect, such as x ~ mu sex !r animal, am I right to
assume that in the case of missing values for ?sex? the MVREMOVE option
should be always avoided because it would then assign all missing sexes as
males, or all as females?
** MVREMOVE discards the RECORD containing the with the unknown sex,
rather than use the record.
MVINCLUDE may assign missing to one sex or the other, or may define a
third 'sex' depending on whats in the model.
Consider the DESIGN matrix
mu Male Female
1 1 0 for a MALE
1 0 1 for a female
1 0 0 for an unknown.

Now the usual model singularity (mu = Male + Female) is broken so ASReml
will fit 2 DF for SEX and 1 for mu,
that is, the missing sexes become a third sex class.

Using MVREMOVE sometimes messes up the record pattern in multivariate
analyses and should be used with care in that context.

Thanks in advance for any answer,
May Jesus Christ continue to be gracious to you,

Arthur Gilmour, His servant .
 
Mixed model regression mapping for QTL detection in experimental crosses.
Computational Statistics and Data Analysis 51:3749-3764 at
http://dx.doi.org/10.1016/j.csda.2006.12.031

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Received on Fri Oct 22 2008 - 08:00:51 EST