kdebusk wrote:
What test do I use to determine if there is a correlation between a
discrete variable and a continuous variable?

For example - I have water quality ratings for streams (excellent,
good, fair, poor) and a corresponding nitrogen concentration for each
rating. I want to know if the the ratings correlate with the
concentration of nitrogen in the stream.

Here you have an ordinal and a continuous variable. The appropriate correlation 
method is polyserial (see polycor package) if you can assume that your 
categories arise from a normal distribution.

Jim

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