I am conducting a research in the field of economics. Based on empiric data I have obtained a multivariate regression function as follows:

F = – 65,9569 + 5,08x – 0,83y – 5,27z + 6,65wwhere F is the dependent variable and x,y,z and w the independent variables.

Is it possible to determine the concavity or convexity of this function? How?

Thanks