cool thanks... so if i were to plot each of the significant terms from the GLM output then the intercept would have to be included for each one?

ie... the intercept is 0.25;

- factor x has coefficient of 0.5, thus a line of y=0.5x + 0.25

- interacting factor x*z has a coefficient of 0.4, thus a curve of y=0.4(x^2) + 0.25

- a further interacting factor x*z*a has a coeff. of 0.1; thus a curve of y=0.1(x^3) + 0.25

does that seem to make sense?

thanks

andy