Hi Mike,
Sorry for the delay on this. ?I'm not sure you want "multinomial3" as your
family given that the three response variables are normally distributed.
Specifying family=rep("gaussian", 3) would be more appropriate. ?You will
still get an error message because the default ?residual term is ~units
which specifies a residual for each row of the response. For univariate
models this is equivalent to IID residuals. For multi-response models it is
more usual to allow different residual variances for each response, and
often residual covariances between responses. rcov=~idh(trait):units fits
different variances across responses (trait) ?but sets the covariances to
zero. rcov= ~us(trait):units ?estimates the covariances too. There are other
less general possibilities too (see CourseNotes) which may be usefull. For
example ?rcov=~trait:units fits a common variance across responses and fixes
the covariances to zero.
Having random=~sid also assumes that each sid effect is identical across
responses so you may want to relax this assumption as above.
Cheers,
Jarrod
On 17 Jun 2010, at 13:43, Mike Lawrence wrote:
Hi folks,
I'm trying to do a mixed multinomial model with 3 response variables,
but I'm getting the error "please use idh() or us() error structure".
I believe that idh() and us() are used to specify the nature of the
interaction between multiple random variables, but I don't have
multiple random variables, so I'm not sure why I'm getting that error.
Some example data are below, but note that in my real data, the dv's
are indeed non-independent (they are in fact the number of trials
classified into each of three categories).
a = expand.grid(
? ? ? ?sid = 1:20
? ? ? ?, condition = factor(1:2)
)
a$group = factor(a$sid%%2)
a$sid = factor(a$sid)
a$dv1 = rnorm(nrow(a))
a$dv2 = rnorm(nrow(a))
a$dv3 = rnorm(nrow(a))
MCMCglmm(
? ? ? ?cbind(dv1,dv2,dv3)~condition*group
? ? ? ?, random = ~ sid
? ? ? ?, family = 'multinomial3'
? ? ? ?, data = a
)
--
Mike Lawrence
Graduate Student
Department of Psychology
Dalhousie University
Looking to arrange a meeting? Check my public calendar:
http://tr.im/mikes_public_calendar
~ Certainty is folly... I think. ~