Thanks Joshua for the clear explanation.

I've previously posted in r sig mixed, but I got no response... :(

Cheers,

- Camila

On Mon, Jul 2, 2012 at 9:31 PM, Joshua Wiley <jwiley.psych@gmail.com> wrote:

> Hi Camila,
>
> In mixed equation form instead of multilevel, it would be:
>
> Y_it = gamma_00 + gamma_10*X_it + gamma_11*W_it*X + (e_it + u_0t + u_1j*X)
>
> your code seems reasonable.  Note that the random intercept and slope
> will be correlated in your specification (unstructured if you want, it
> is possible to force out, but is sensible starting place)
>
> model <- lmer(Y ~ X + X:W + (X | ID), data = data)
>
> which gives:
> residual variance: e_it
> variance of intercept (constant term, gamma_00): u_0t
> variance of slope (gamma_10): u_1j*X
>
> as well as overall estimates for the intercept, slope of X, and the
> interaction of X and W.
>
> Bert is correct that R sig mixed models is the more appropriate list,
> but many people read both and there is no reason it cannot be answered
> here.
>
> Cheers,
>
> Josh
>
>
> On Mon, Jul 2, 2012 at 6:47 PM, Camila Mendes <cacamendes85@gmail.com>
> wrote:
> > Hey all -
> >
> > I am a newbie on mixed-effects models. I want to estimate the following
> > model:
> >
> > Y_it = alpha_0t + alpha_1t*X_it + e_it
> > alpha_0t = gamma_00 + u_0t
> > alpha_1t = gamma_10 + gamma_11*W_it + u_1j
> >
> > Where Y is my outcome, X is my level-1 predictor, and W is my level 2
> > predictor.
> >
> > I am not sure if I am doing it right. Is this the correct specification
> of
> > the formula?
> >
> > model = lmer(Y ~ X + X:Y + ( X | ID), data = data)
> >
> > Also, can you help me to write down the combined model formula? I tried
> > by substituting on the first equation, but I got some weird interactions
> > with the residual (?)
> >
> > Thanks a lot!
> >
> > - Camila
> >
> >         [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Joshua Wiley
> Ph.D. Student, Health Psychology
> Programmer Analyst II, Statistical Consulting Group
> University of California, Los Angeles
> https://joshuawiley.com/
>

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