A data set from Oehlert (2000) \emph{A First Course in Design and
Analysis of Experiments}, New York: W. H. Freeman.

Data originally from Nelson, T.~S., L.~K. Kriby, and Z.~B. Johnson (1990).
``Effect of minerals on the incidence of leg abnormalities in growing
broiler chicks.'' {\em Nutrition Research\/}~{\em 10}, 525--533.

Table of treatment means. Columns are available phosphorus levels (.25 or .5%)
Rows are available calcium levels (.6, .9, 1.2%).) Each response is average
body weight (g) for 4 pens of chicks.