Counts of mayfly nymphs at low flow in 12 small streams. In each stream, counts were recorded above and below industrial outfalls.
A data frame with 24 observations on the following 3 variables.
Number of mayfly nymphs counted
a factor indicating the stream number
a factor indicating the location of the count (above vs. below)
Helsel, D.R., and R.M. Hirsch. (2002). Statistical Methods in Water Resources Research. Techniques of Water Resources Investigations, Book 4, Chapter A3. U.S. Geological Survey, 139–140. http://water.usgs.gov/pubs/twri/twri4a3/.