[R-sig-ME] Baseline + Follow-Up

[Isabella Ghement]

Thank you so much, Douglas!  I am not familiar with the "0" trick - can you
provide me with
some intuition for why this might work?

Isabella


-----Original Message-----
From: dmbates at gmail.com [mailto:dmbates at gmail.com]On Behalf Of Douglas
Bates
Sent: February 3, 2010 9:40 AM
To: Isabella Ghement
Cc: r-sig-mixed-models at r-project.org
Subject: Re: [R-sig-ME] Baseline + Follow-Up


On Wed, Feb 3, 2010 at 11:12 AM, Isabella Ghement <isabella at ghement.ca>
wrote:
> Hi everyone,
>
> I am using the lme() function in the nlme library to fit a linear mixed
> effects model
> such as the one below, where an individual-level follow-up measurement is
> modeled as a linear
> function of an individual-level baseline measurement plus a fixed
treatment
> effect
> plus a random cluster effect plus random error:
>
> lme(FollowUp ~ Baseline + Treatment, random=~1|Cluster, method="REML",
> data=Data)
>
> The summary of the lme model fit reports a point estimate and confidence
> interval
> for the treatment effect (i.e., difference in adjusted treatment means),
but
> I am also
> interested in getting estimates and confidence intervals for the adjusted
> treatment means.
> In my case, Treatment is a factor having two levels (say, A and B).
> Is there a way to force lme() to report these quantities?

If I understand what you are asking, you can get these standard errors
by modifying the formula to

FollowUp ~ 0 + Treatment + Baseline