st: -mfx-: can I just keep the interaction variable?

[Scott Cunningham <scunning@gmail.com>]

I estimated a poisson model with a dummy variable plus 60 fixed  
effects.  I want to report the marginal effects for five variables,  
one of which is a dummy variable ("race").  The Stata output lists  
the variable as "_Irace_2", but when I used the following command:

mfx, dydx varlist(_Irace_2 covariate1 covariate2 covariate3 covariate4)

I got this error:

no observations
r(2000);

The help on r(2000) says that I have "requested some statistical  
calculation and there are no observations on which to perform it.   
Perhaps you specified if exp or in range and inadvertently filtered  
all the data."

I'm assuming that the problem is with the name of the race dummy - it  
must not be recognizing "_Irace_2" in the varlist.  Yet I've not seen  
anywhere in mfx as to how to call for a dummy variable's marginal  
effect.  Is it not the same name that is reported in the raw output?

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