[S] Mixed Model with AR(1) errors

Regula Schwager-Suter (suter@inw.agrl.ethz.ch)
Tue, 15 Sep 1998 14:03:04 +0200

I am using S-Plus, Version 3.4 Release 1 for Sun SPARC, SunOS 5.3

I have repeated measures data on several animals. Because the data are
collected over time, there could be correlation between serial observations
on the same experimental unit.
Chi and Reinsel (1989) give the following approach for one individual:

Y = Xb + Ct + u

with Xb the fixed part of the model, Ct the random part and u the
within-individual errors whose components are assumed to follow the AR(1)model

u(t) = phi*u(t-1) + e(t) e(t)~N(0, sigma^2) t = time of data collection

So I used the following model in S-Plus to analyze my data:

model_lme(fixed = Y ~ C(effect1, treatment) + C(effect2, treatment) +
C(effect3, treatment) + covariate1 + covariate2 + covariate3 + ... +
covariate8, random= ~1, cluster= ~subject, serial.structure="ar1",
serial.covariate= ~week)

I now would like to have a look at the distribution of the appropriate
residuals (u's and e's in Chi & Reinsel's model) in the S-Plus output. Can
I do this and if yes how can I do this?

Thank you very much for your help!


Regula Schwager-Suter
Swiss Federal Institute of Technology
Institute of Animal Science
Animal Breeding
Clausiusstrasse 50
CH-8092 Zürich
phone: +41 (0)1 632 39 56
fax: +41 (0)1 632 12 60
e-mail: suter@inw.agrl.ethz.ch
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