On Mon, Nov 21 2011, Vincenzo Carrieri wrote:
> Stata gives me only two marginal effects: one for age and one for
> income.
Surely that's because you have only two variables.
What your model gives you is a surface in three dimensions (prediction
by age by income) that is multiply non-linear (probit, quadratic,
interaction). As I understand it, -margins- averages this surface across
the data in some sense (in different ways depending on what you ask it).
Surely the advantage of -margins- is reducing messy non-linear models to
relatively simple summaries, and not in reproducing something equally
complex (in terms that may be inconsistent with the underlying
functional form)?
(That was a question rather than a statement: I sometimes think I'm not
quite getting marginal effects.)
Brendan
--
Brendan Halpin, Department of Sociology, University of Limerick, Ireland
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