On Thu, Oct 16, 2008 at 8:05 AM, kdebusk <[EMAIL PROTECTED]> 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.
What does correlation mean in this example? How can you interpret a linear correlation when one of your variables is discrete? Why not start with some exploratory graphics? For your case, I would suggest drawing a histogram of nitrogen concentration for each water quality. Then look at the histograms - do they look the same? Do they look different? If they are different, what features are different? Hadley -- http://had.co.nz/ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
