R help - Feb 2006 - need help on nlme()

Hello there,

I am using nlme() to fit a logistic mixed effect model on our data.
The outcome variable is binary.
I got the error when I wanted to add a group factor to my model.

My initial model is as below:

model.a <- nlme(response~ 1/(1 + exp( -intercept- u0 - slope*TIME -
u1*TIME)),
                           + fixed=intercept+slope~1, random= u0+u1~1
|studentID,
                           + start=c(slope=.01, intercept=-1), data=log.data,
method='ML')

This works fine on my data. But when i update it by adding a group factor
SKILLS,
I got the error message:
"Error in nlme.formula(response ~  1/(1 + exp( -intercept- u0 - slope*TIME
:
        starting values for the fixed component are not the correct length"

The model is as below:
model.a <- nlme(response~ 1/(1 + exp( -intercept- u0 - slope*TIME -
u1*TIME)),
                           + fixed=intercept+slope ~ SKILLS, random= u0+u1~1
|studentID,
                           + start=c(slope=.01, intercept=-1), data=log.data,
method='ML')

Does anybody see anything wrong with the "start" part of this model?

Thanks a lot!!

	[[alternative HTML version deleted]]

I think nlme is not for logistic mixed effect model.
you should use glmmPQL in MASS or lmer in Matrix

2006/2/20, Mingyu Feng <mingyufeng at gmail.com>:
> Hello there,
>
> I am using nlme() to fit a logistic mixed effect model on our data.
> The outcome variable is binary.
> I got the error when I wanted to add a group factor to my model.
>
> My initial model is as below:
>
> model.a <- nlme(response~ 1/(1 + exp( -intercept- u0 - slope*TIME -
> u1*TIME)),
>                            + fixed=intercept+slope~1, random= u0+u1~1
> |studentID,
>                            + start=c(slope=.01, intercept=-1),
data=log.data,
> method='ML')
>
> This works fine on my data. But when i update it by adding a group factor
> SKILLS,
> I got the error message:
> "Error in nlme.formula(response ~  1/(1 + exp( -intercept- u0 -
slope*TIME
> :
>         starting values for the fixed component are not the correct
length"
>
> The model is as below:
> model.a <- nlme(response~ 1/(1 + exp( -intercept- u0 - slope*TIME -
> u1*TIME)),
>                            + fixed=intercept+slope ~ SKILLS, random=
u0+u1~1
> |studentID,
>                            + start=c(slope=.01, intercept=-1),
data=log.data,
> method='ML')
>
> Does anybody see anything wrong with the "start" part of this
model?
>
> Thanks a lot!!
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
>

--
伝伷伻佡伖侒
Deparment of Sociology
Fudan University