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
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