Continuous variables in 3 dimensions
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Continuous variables in 3 dimensions

Dear All
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 surface.
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 surface?
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 problem.
Any ideas please?
Dr Geoff Pollott
Senior Lecturer in Animal Breeding and Production
Department of Agricultural Sciences
Imperial College at Wye
TN25 5AH

Tel: +44 (0)20 759 42707
Fax: +44 (0)20 759 42919