[R] Random Effects Model

[readams at colby.edu]

Hello,

I am new to R, and I am trying to figure out how to use it for a  
random effects model. I am using version 2.4.0, and I also have the  
book Applied Linear Regression by Sanford Weisberg.

I have four variables: Swimmer, Sex, Swim, and Difference.  Swimmer  
identifies the number assigned to a particular person. Sex is  
male/female. Swim identifies the number swim from 1 to 6. Difference  
is my variable of interest (random).

The book says I should run something like this:

> library(nlme)
> data(FREE) #FREE is my dataset
> xyplot(Difference~Swim|Type, group=Swimmer, data=FREE,
+     panel.groups=function(x,y,...){
+       panel.linejoin(x,y,horizontal=FALSE,...)}
+     )
> m1 <- lme(Difference~Swim+Type, data=FREE, random=~1+Type|Swimmer)
> m2 <- update(m1, random=~1|Swimmer)

I've pretty much decided that xyplot doesn't work. Instead, I think  
plot will work much better.  I keep getting errors about Type. Can  
someone explain this to me? Does the code above look right?

Any kind of help will be appreciated...

Thanks in advance!

Ryan