[R] advise for modeling a linear mixed model

[Frank Mattes]

Dear R help-list reader,

I'm trying to investigate my data with linear mixed model and are 
seeking advise how to write the model in R. I was trying to get hold 
of the recommended book from Bates et al, but neither the major 
bookshop nor our university library had the book. My data is 
mirroring the example given in the appendix of John Foxes book 
"Applied Regression" with a small exception.

I'm interested in a frequency (freq) of a particular cell type which 
was measured longitudinal in patients (p) and  control group (c). In 
addition, each sample was measured four times (repeat) with a 
possible factor influencing the sensitivity (gated).

Here my data frame:

ID	freq	day	repeat	group	gated
1	0.1	1	1	c	10000
1	0.15	1	2	c	12000
1	0.2	1	3	c	50000
1	0.1	1	4	c	12000
1	0.5	12	1	c	12000
1	0.1	12	2	c	50000
1	0.2	12	3	c	100000
1	0.4	12	4	c	70000
1	0.2	5	1	p	15000
2	0.25	5	2	p	6000
2	.
2	.

So I could write a model with a fixed effects for day and group and 
their interaction.

lme(freq ~ day*group, random = ~day | ID data=frame)

I'm expecting possible effect of "gated" on the frequency. I don't 
know how to include the fact that I have four measures from the same 
sample and an effect of the variable "gated" on the frequency.

I'm appreciate any help, and apologize in case I have not read 
carefully the available documentation.

Frank
-- 
Frank Mattes				e-mail:	f.mattes at ucl.ac.uk
Department of Virology			fax	0044(0)207 8302854
Royal Free Hospital and 			tel	0044(0)207 8302997
University College Medical School
London