[R] parameterisation of Factor levels

[MJ Price, Social Medicine]

Hi all,

I am trying to fit simple 2 factor (factors A and B - 3 and 2 levels 
respectively) poisson regression model. Inititially a pure error model is 
fitted and significance tests are performed on each parameter. I wish to 
remove an individual parameter from the model - the interaction between the 
second level of factor A and factor B. However i only seem to be able to 
remove the AB (all interactions between A and B) term, which is no use as 
it also removes the interaction term between level 3 of Factor A and factor 
B. Can anyone help with this.

Thanks

Malcolm

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MJ Price, Social Medicine
epmjp at bristol.ac.uk