Re: Wilmik and random regression

From: Nicola Macciotta <macciott_at_UNISS.IT>
Date: Mon, 10 Oct 2005 17:13:22 +0200

thank you for your answer but probably I have not been very much clear in
my question. The RR model I am trying to fit is

Milk (daily yield) = HTD AGE DIM ANIMAL


HTD = effect of a specific combination of herd-test date
AGE = covariable represented by the age at calving
DIM = fixed effect of the stage of lactation (10 intervals of 30 days each)
to account for the average lactation curve

is the fixed part of the model

for the random part ANIMAL, I would like to model individual deviations
using different functions in order to test the effects of the function used
on the estimated patterns of variances along the lactation. Among the
function, apart from those that are currently used as Legendre Polynomials,
I would like to use some common linear (or linearisable) functions of
lactation curve such as the Wilmink model (that was used in one of the
earlier version of the Canadian RRM). I will use it in the linear form
because I am setting the k parameter to a fixed value (that I have
previously estimated by fitting the non-linear form). I am previously
interested in estimating the (co)variance matrix of random coefficients.
But my problem is how to enter the Wilmink function as random term in ASREML.



probablyAt 15.03 10/10/2005, you wrote:
>Wilmik's curve is not random regression but rather a nonlinear function like
>other functions such as Wood's. Apart from the nonlinear generalized linear
>models, these models can not be fitted as such in ASREML. In the case of
>if the c parameter is treated as known then it becomes a simple linear
>model and
>can be fitted. However, this is usually rather stupid because biases the
>results. Also if you knew this parameter then there is no need to fit the
>---- Original message ----
> >Date: Thu, 6 Oct 2005 12:54:23 +0200
> >From: Nicola Macciotta <macciott_at_UNISS.IT>
> >
> >Dear ASREML users,
> >I am trying to run a random regression model for milk yield where I would
> >like to test for modeling individual random deviations wioh different
> >functions, some of them are not implemented in the ASREML software. For
> >example, the function proposed by Wilmink (1987, Liv. Prod. Sci.)
> >
> >Ydim= a + be-kdim + cdim
> >
> >where dim are the days in milk. The function can be linearised by setting k
> >to a fixed value (0.1 for example).
> >
> >So the model I want to use has three terms
> >
> >a the intercept
> >
> >b that actually is (be-0.1dim )
> >
> >
> >c x dim
> >
> >So my question is: how can I put this function as random within animal?
> >Could be this the correct syntax of the random part of the model?
> >
> >r! a.animal b.animal dim.animal
> >
> >
> >and how can I get the (co)variance matrix of coefficients?
> >
> >
> >Thank you very much for your help
> >
> >Nicol˛
> >
> >Nicol˛ P.P. Macciotta
> >Dipartimento di Scienze Zootecniche
> >UniversitÓ degli Studi di Sassari
> >Via De Nicola, 9
> > 07100 Sassari, Italia
> >tel 39.079.229298 fax 39.079.229302
> >e-mail

Nicol˛ P.P. Macciotta
Dipartimento di Scienze Zootecniche
UniversitÓ degli Studi di Sassari
Via De Nicola, 9
  07100 Sassari, Italia
tel 39.079.229298 fax 39.079.229302
Received on Sun Oct 10 2005 - 17:13:22 EST

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