[R-sig-ME] MCMCglmm troubles
j.hadfield at ed.ac.uk
Thu Jun 24 10:46:59 CEST 2010
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.
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))
> , random = ~ sid
> , family = 'multinomial3'
> , data = a
> Mike Lawrence
> Graduate Student
> Department of Psychology
> Dalhousie University
> Looking to arrange a meeting? Check my public calendar:
> ~ Certainty is folly... I think. ~
> R-sig-mixed-models at r-project.org mailing list
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