Dear all,
I have a question about baseline category logits.
My data is about colors of infant stools.
Stools can be brow, green or yellow.
Color of stools is collected at 4 visits.
However, at visits only marginal information
is available, not the sequence of color.
E.g. sequence: YYYYYBYBY is collapsed to 2B, 0G, 7Y.
Infants are randomized to two infant formula groups
(for1, for2) in a factorial design. Question of
interest is, whether one of the two formula can
influence the color of stools.
The data looks like:
for1 for2 visit1 visit2 visit3 visit4
----------------------------------------------------
subj | | | B G Y | B G Y | B G Y | B G Y
------------------------------------------------
1 | 0 | 0 | 2 0 7 | 0 0 5 | 0 0 3 | 0 0 4
2 | 0 | 0 | 0 0 13 | 0 2 15 | 0 0 13 | 0 0 10
3 | 0 | 1 | 1 1 17 | 0 0 17 | 1 0 10 | 0 0 9
4 | 0 | 1 | 0 0 10 | 0 0 10 | 0 5 11 | 0 6 9
...
31 | 1 | 0 | 2 0 7 | 0 0 1 | 0 0 0 | 0 0 0
32 | 1 | 0 | 0 0 3 | 0 0 5 | 0 0 3 | 0 0 5
33 | 1 | 1 | 0 0 10 | 0 0 11 | 0 0 3 | 0 0 3
34 | 1 | 1 | 0 0 9 | 0 0 9 | 0 0 8 | 0 0 3
...
I am thinking of a baseline category logits model
like Agrestis Alligator Food Choice Example in the
(1996) book, but additional with some time dependency.
Perhaps, random effects could be useful
to model time dependency.
Alternatively, I can handle every color as a separate
variable, doing three separate longitudinal analysis,
one of yellow stool counts, one for green stool counts
and one for brown stool counts.
Every help would be appreciate,
perhaps someone could point me to a similar example.
Kind regards,
Dominik
Dominik Grathwohl
Biostatistician
Nestl? Research Center
PO Box 44, CH-1000 Lausanne 26
Phone: + 41 21 785 8034
Fax: + 41 21 785 8556
e-mail: dominik.grathwohl at rdls.nestle.com
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