[R] 2x2 Contingency table with much sampling zeroes

[Etienne Toffin]

Hi,

I'm analyzing experimental results where two different events ("T1"  
and "T2") can occur or not during an experiment. I made my experiments  
with one factor ("Substrate") with two levels ("Sand" and "Clay").
I would like to know wether or not "Substrate" affects the occurrence  
probability of the two events. Moreover, for each condition I would  
like to test the heterogeneity of my experimental contingency table  
with a theoretical one (from simulations).

However, my problem is that several cells have sampling zeroes. My  
experiments can't be done again to fill these cells. Thus Chi-square  
requirements are not fulfilled and I have to find another statistical  
method.

After spending hours searching for a solution, I thought I could use  
loglinear model to answer my questions, but :
- I'm not sure I can use loglinear model = do I fulfill the required  
conditions ?
- would this method answer to my hypothesis ?
- I not sure to really understand how I have to use loglin()…

Here is the data frame of my results.

DF<-data.frame(Subs=c(rep("Sand",4),rep("Clay",4)),T1=rep(c 
("YES","YES","NO","NO"),2),T2=rep(c("YES","NO","YES","NO"),2),Freq=c 
(12,5,0,7,24,1,0,0))

What do you think of such datas ? Can I use any statistical method to  
test my hypothesis ? Any advice ?

Thanks,

Etienne Toffin


-------------------------------------------------------------------
Etienne Toffin, PhD Student
Unit of Social Ecology
Université Libre de Bruxelles, CP 231
Boulevard du Triomphe
B-1050 Brussels
Belgium

Tel: +32(0)2/650.55.30
Fax: +32(0)2/650.57.67
http://www.ulb.ac.be/sciences/use/toffin.html