I performed with SAS an ANOVA and I got insignificant differences for each coefficient. So I planed to looked at the linear and quadratic effects of the Ca concentration (6 levels), and the linear was not significant, but the quadratic was. I remember for multiple comparison, it is always require an significant model to do the next step.
Is it the same situation for orthogonal contrast? Does it makes sense to have significant contrast effects but no main effects?