Message-ID: <40e66e0b0712071404o457376fcx7644c694a60518a3@mail.gmail.com>
Date: 2007-12-07T22:04:21Z
From: Douglas Bates
Subject: QQ Norm
In-Reply-To: <40e66e0b0712071015wf84e875uc5cac668332e92c8@mail.gmail.com>
On Dec 7, 2007 12:15 PM, Douglas Bates <bates at stat.wisc.edu> wrote:
> On Dec 7, 2007 11:18 AM, Roberts, Kyle <kyler at mail.smu.edu> wrote:
> > Just a simple yes or no. Is there any difference between:
> >
> > qqnorm(resid(lmer.out))
> > and
> > qqmath(~resid(lmer.out))
>
> That's a bad question for which to say that you want a simple yes/no
> because the answer is obciously yes and now you are going to need to
> ask what the differences are.
I was being facetious with that answer. There are obvious differences
in that qqnorm is a standard graphics function and qqmath is
lattice/grid. Other than that there isn't really a difference.
The only class of objects for which the lme4 package defines a special
qqmath method is the ranef classes, such as ranef.mer and ranef.lmer.
For those classes the method creates a form of "caterpillar plot" if
you ask for the posterior variances (which, if I had it to do over
again, I would call "conditional variances") to be returned (i.e.
postVar = TRUE).
By the way, it is now possible to omit the ~ in the first argument for
qqmath so you could write
qqmath(resid(lmer.out))
Whether it is advisable to do so is something I still haven't decided
for myself.