st: Marginal effects with an Heckman selection model

[fabio.sigismondi@ulg.ac.be]

Dear statalist, 

I'm estimating the charitable giving of households thanks to administrative data's. To do so I'm estimating an exponential Heckman selection model (Wooldridge, 2nd edition, chapter 17) with the two step procedure. 

Here is my model : 
heckman lnlib i.ageet  i.rq2  i.sociomen3 i.region i.ep  i.rcb price  , select(lib = i.ageet  i.rq2  i.sociomen3 i.region i.gendre i.ms i.child i.prop  i.avb   i.ep  i.rcb price )  two 

I want to estimate the marginal impacts of my variables on the probability of giving to charities and on the amount given. Because I'm using stata 11, I think I should use the margins option but I don't really understand what this option does with an Heckman selection model. 

To estimate the marginal effects on the probability, I estimate the probit model and I use 
margins, dydx (ageet). Am I right to do that? 


How can I compute the impact on the amount given? should I use for example margins, dydx (ageet) after the estimation of the Heckman selection model? 

Thanks in advance for the help 

Fabio S. 
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