I have had several
situations recently where I am interested in analysing a dependent variable (D)
and two independent varaibles (I1 and I2) in the same model, all three being
continuous, normally distributed etc.
D = a + b(I1) +
c(I2) + ........
The plot of this
relationship is of course three dimensional and a flat
If I suspect that
the response surface is not flat:
a) Has anyone got
any ideas for a left hand side that could explore the curvature of the response
b) Has anyone got
any good software for plotting such a surface in 3D.
My 'simple' solution
is to divide each independent variable into a number of classes and then
estimate the interaction least-squares means for each sub-class. These can be
plotted. However, this seems rather a 'cop out' way of solving the
_____________________________________________________ Dr Geoff Pollott Senior Lecturer in Animal Breeding and
Production Department of
Agricultural Sciences Imperial
College at Wye Ashford Kent TN25