R help - Jul 2010 - xyplot: key inside the plot region / lme: confidence bands for predicted

I have two questions related to plotting predicted values for a linear 
mixed model using xyplot:

1:  With a groups= argument, I can't seem to get the key to appear 
inside the xyplot. (I have the Lattice book,
but don't find an example that actually does this.)
2: With lme(), how can I generate confidence bands or prediction 
intervals around the fitted values?  Once
I get them, I'd like to add them to the plot. 

Example:

library(nlme)
library(lattice)
Ortho <- Orthodont
Ortho$year <- Ortho$year - 8  # make intercept = initial status

Ortho.mix1 <- lme(distance ~ year * Sex, data=Ortho,
        random = ~ 1 + year | Subject, method="ML",
#        correlation = corAR1 (form = ~ 1 | Subject)
        )
Ortho.mix1

# predicted values
grid <- expand.grid(year=0:6, Sex=c("Male", "Female"))
grid$age <- grid$year+8  # plot vs. age
fm.mix1 <-cbind(grid, distance = predict(Ortho.mix1, newdata = grid, 
level=0))

xyplot(distance ~ age, data=fm.mix1, groups=Sex, type="b",
pch=c(15,16),
cex=1.2,
    auto.key=list(text=c("Male", "Female"), points = TRUE,
x=8, y=26),
    main="Linear mixed model: predicted growth")

Can someone help?

-Michael

-- 
Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    Web:   http://www.datavis.ca
Toronto, ONT  M3J 1P3 CANADA

On 2010-07-02 9:37, Michael Friendly wrote:
> I have two questions related to plotting predicted values for a linear
> mixed model using xyplot:
>
> 1: With a groups= argument, I can't seem to get the key to appear
inside
> the xyplot. (I have the Lattice book,
> but don't find an example that actually does this.)
> 2: With lme(), how can I generate confidence bands or prediction
> intervals around the fitted values? Once
> I get them, I'd like to add them to the plot.
> Example:
>
> library(nlme)
> library(lattice)
> Ortho <- Orthodont
> Ortho$year <- Ortho$year - 8 # make intercept = initial status
>
> Ortho.mix1 <- lme(distance ~ year * Sex, data=Ortho,
> random = ~ 1 + year | Subject, method="ML",
> # correlation = corAR1 (form = ~ 1 | Subject)
> )
> Ortho.mix1
>
> # predicted values
> grid <- expand.grid(year=0:6, Sex=c("Male",
"Female"))
> grid$age <- grid$year+8 # plot vs. age
> fm.mix1 <-cbind(grid, distance = predict(Ortho.mix1, newdata = grid,
> level=0))
>
> xyplot(distance ~ age, data=fm.mix1, groups=Sex, type="b",
pch=c(15,16),
> cex=1.2,
> auto.key=list(text=c("Male", "Female"), points = TRUE,
x=8, y=26),
> main="Linear mixed model: predicted growth")
>
> Can someone help?
>
> -Michael

Michael,

the x,y location should be specified in the unit square
(and you might want to set the 'corner' component).

  Ortho$year <- Ortho$age - 8 ##fix typo
  xyplot(distance ~ age, data=fm.mix1, groups=Sex,
         type="b", pch=c(15,16), cex=1.2,
         auto.key=list(text=c("Male", "Female"),
                       points = TRUE,
                       x=0.1, y=0.8, corner=c(0,1)))

See description of 'key' in ?xyplot.

   -Peter Ehlers