[R] ANOVA: New User question

[Peter Dalgaard]

Mackay Peter wrote:
> I am a relatively new user of R, and have a question on ANOVA
>
> I have a sumamrised data set of the form (data dummy only) 
>
> Cell	Treatment	Total	Resp		
> 1	1		25000	682	
> 1	0		35000	600	
> 2	1		5000	40	
> 2	0		4000	30	
> 3	1		36000	2400	
> 3	0		400	250	
>
> and wish to perform ANOVA. Because its sumamrised I need to tell R to
> treat the data as if I had all the individual rows. Otherwise, I only
> end up with 1 or 2 DF.
>
> I know in SAS, ANOVA has a 'FREQ' option ... does something similar
> exist in R?
>
>   
An explicit rep(x, count) does the same as the FREQ option. Without the
group standard deviations, neither will produce anything useful, though.

If you do have SDs, there's a technique used in my book

fake.trypsin<-local({
xrnorm<-function(n,xbar,s){
        t<-rnorm(n);t<-(t-mean(t))/sd(t);xbar+s*t}
g.1<-xrnorm(32,128,50.9)
g.2<-xrnorm(137,152,58.5)
g.3<-xrnorm(38,194,49.3)
g.4<-xrnorm(44,207,66.3)
g.5<-xrnorm(16,215,60)
g.6<-xrnorm(4,218,14)
trypsin<-c(g.1,g.2,g.3,g.4,g.5,g.6)
grp<-rep(1:6,c(32,137,38,44,16,4))
grpf<-factor(grp)
data.frame(trypsin,grp,grpf)})

or you can use the equivalent of this SAS trick:

http://ssc.utexas.edu/consulting/answers/sas/sas48.html

-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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