Greetings to all, and my apologies for a question that is mostly about
statistics and secondarily about R.  I have just started a new job that
(this week, apparently) requires statistical knowledge beyond my training
(as an epidemiologist).

The problem:

- We have 57 food production facilities in three categories
- Samples of 4-6 different foods were tested for listeria at each facility
- I need to describe the presence of listeria in food (1) overall and (2) by
facility category.

I know that samples within each facility cannot be treated as independent,
so I need an approach that accounts for (1) clustering within facilities and
(2) the different number of samples taken at each facility.  If someone
could kindly point me towards the right type of analysis for this and/or its
associated R functions/packages, I would greatly appreciate it.

Many thanks,

Sarah

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