Help with inflection point in a curvilinear relationship

[Iconia]

Hi all,

I am reading an article that does a panel poission regression and finds out the following function:

Y= 2,22 + 0,08X1 -0,0001 X1SQ +1,42* X2 -4,17* X2SQ+1,24 X3

both X1 and X2 have quadratic terms (I put SQ). then the article goes on to indicate the inflection point (on y axis) for variable X1 and then X2.

Could anyone please help me how to find the inflection point bwith poission regression? I understand that one differentiates the equation based on X1 (or X2) and then equates to zero; takes the value that leads to zero and then plugs into the equation above to find the inflection value on Y...But I cant get the numbers the authors write. What am I missing?
Thank you very much
PS: I will be more than happy to email the article

[JohnM]

Have you tried contacting the authors? I'm sure they'd be thrilled to hear from someone who actually read their article and wants to discuss it....