[Limdep Nlogit List] Marginal effects in a random parameter model

[Jaap Bos]

Dear all,

I have estimated the following specification:

frontier;lhs=tc;rhs=one,x1,x2,y1,y2;pds;fcn=y1(N),y2(N);rpm=y1_,y2_;cost$

Where y1_ and y2_ are the firm specific means for y1 and y2.

Now i want to calculate the marginal effects for x1, x2 and y1 and y2 for all firms (>5000) in my data set. 

My general question is: how to go about to do this?

More specifically:

(a) Is the average marginal effect for y1, the coefficient on y1 + the scale parameter for y1 * y1_ + scale parameter for y2 * y2_ ?

(b) Do i need the "Heterogeneity in the means of random parameters" to adjust for correlations among my z's?

gr + thanks, Jaap Bos