Hi all,



Being new to analysing epidemiologic data, I have a question about the following data set:

A friend has inspected three randomly chosen farms (random factor 'farm'). At each farm three randomly chosen series of chickens (random factor 'flock') were each inspected for the presence of a certain bacteria. The contaminated chickens were counted (response variable 'positives'). The sample sizes per flock are given by 'broilers'. We want to have a look at within-broilers, within-farm and between-farm variability.



It seems to me that we have a random-effects model, in which the factor 'flock' is nested within the factor 'farm'. Am I correct so far?

Now, since the response variable yields count data, fitting the model should be done using Poisson regression. Correct?



Could somebody help me out with (an example of) such an analysis?



Many thanks in advance,

Dieter



Here is the dataset used:



broilers<-data.frame(farm=c("FA","FA","FA","FB","FB","FB","FC","FC","FC"), flock=c("a","b","c","d","e","f","g","h","i"), broilers=c(50, rep(25,8)), positives=c(7,2,0,7,2,0,0,5,2))





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Dieter Anseeuw

Katho Campus Roeselare

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8800 Roeselare Belgium



Direct phone: +32 51 23 29 68

http://www.katho.be/hivb

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