[R] Cross-over Data with Kenward-Roger correction

[Ben Bolker]

knouri <nouri4 <at> yahoo.com> writes:

> 
> Dear all:for the folowing data, a two-period, two treatment (A=1 vs. B=2)
> cross-over is fitted
> using the folowing SAS code.  
> data one;

[snip]

> run;
> proc mixed data=one method=reml;
> class Sbj Per Trt;
>    model PEF = Per Trt /ddfm=kr;
>    repeated Trt / sub=Sbj type=un r;
>    lsmeans Trt / cl alpha=0.05;
>    estimate 'B vs. A' Trt -1  1 / alpha=0.1 cl;
> run;

> (where kr option is for Kenward-Roger method).I need to use R to
> reproduce the results similar to what the above SAS code generates.
> I have used several R functions including lme, lmer with no success
> so far.Any advice will be greatly appreciated,Sincerely, Keramat


This is more appropriate for r-sig-mixed-models at r-project.org.
Please post followups there.

The lmerTest and lsmeans packages will probably be useful.

As a statistical point, I don't understand why you can't just
do a paired t-test on these data??

dat <- read.table(header=TRUE,text=
"Sbj Seq Per Trt PEF
1 1 1 1 310
1 1 2 2 270
4 1 1 1 310
4 1 2 2 260
6 1 1 1 370
6 1 2 2 300
7 1 1 1 410
7 1 2 2 390
10 1 1 1 250
10 1 2 2 210
11 1 1 1 380
11 1 2 2 350
14 1 1 1 330
14 1 2 2 365
2 2 1 2 370
2 2 2 1 385
3 2 1 2 310
3 2 2 1 400
5 2 1 2 380
5 2 2 1 410
9 2 1 2 290
9 2 2 1 320
12 2 1 2 260
12 2 2 1 340
13 2 1 2 90
13 2 2 1 220")

library(lmerTest)
library(ggplot2); theme_set(theme_bw())
ggplot(dat,aes(x=Per,y=PEF,colour=factor(Trt)))+geom_point()+
    geom_line(colour="gray",aes(group=Sbj))+
        scale_x_continuous(breaks=c(1,2))
        
m1 <- lmer(PEF~Per+Trt +(Trt|Sbj), data=dat)

## warning about unidentifiability