Dear all,

I've been trying to model nonlinear relationships in a multilevel model (mixed).

I'm just not really sure how to interpret my findings. In the model with both the linear and the quadratic term
Code:
mixed wag c.SM c.SM#c.SM (other independent variables) || ID:
the linear term is not significiant and the regression coefficient is positive whereas the quadratic term is significant and also positive.
I checked the joint significance via
Code:
test c.SM c.SM#c.SM
which was significant. So I calculated the vertex (-b/2a) which lies in the range of values. Can I assume that I have a U-shaped relationship even though the linear term is not significant and both terms have a positive regression coefficient? I've only found cases in which the regression coefficients were positive/negative or negative/positive for the linear and quadratic term.

Thanks a lot in advance!