Re: radio or variance component for random effect?

Dear luan sheng,

Whether the analysis is performed on variance ratios or components depends
basically on the complexity.

The components are treated as ratios if it is a univariate analysis of a
single experiment unless the user explicitly
defines a residual variance. When there are multiple residuals (as in
multiple trait or multiple experiments),
the analysis is performed in terms of variances (not ratios).

The advantage of using ratios, is that the scale od the data does not
upset the analysis.
When using the variance scale, the data should generally be scaled so that
the variance is between 0.1 and 1000.
Sometimes convergence problems occur when the variances are extremely
small or large.

You example would be analysed on the variance scale if you appended

1 1 0
0 0 IDV 10 !S2==1.0

where 10 becomes the explicit residual variance and 1.0 is the overal
scaling.

This is discussed in the user guide.

NB There is some confusion in the syntax because in mult-site analyses
the !S2 qualifier has a different meaning, in that it sets the residual
variance for the site.

May Jesus Christ 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 now available at
http://dx.doi.org/10.1016/j.csda.2006.12.031

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luansheng <luansheng_at_GMAIL.COM>
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Subject
radio or variance component for random effect?

Dear friends:

 I know from the userguide that the initial value (variance component or
ratio) can be specified after the model term. I use the the following
asreml file to estimate the predictions of random additive genetic effects
(breeding value) . The number of 0.2628 and 0.0116 are the ratios
(relative to the residual variance), respectively.
  My question is that Asreml how to know these numbers are the ratios, but
not the variance components?

Growth traits for chinese shrimp
 animal !P
 sire !P
 dam !P
 familynum 70 !I
 tank 3
 sex 2 !I
 days
 lg
 wt
 meanwt
wt2007.ped !MAKE
wt200712fullsib.txt !SKIP 1 !MAXIT 1

wt ~ mu tank sex days !r animal 0.2628 ide(dam) 0.0116

   Yours sincerely,

   luan sheng
   ----------------------------------------
   Yellow Sea Fisheries Research Institute
   Chinese Academy of Fisheries Sciences
   Nanjing Road 106
   Qingdao 266071
   China
   luansheng_at_gmail.com
   luansheng_at_ysfri.ac.cn
   ----------------------------------------
Received on Fri Oct 29 2007 - 10:07:41 EST