Hi there

Within sampleSelection, I'm trying to calculate the marginal effects for
variables that are present in both the selection and outcome models.

For example, age might have a positive effect on probability of selection,
but then a negative effect on the outcome variable. i.e.
Model<-selection(participation~age, frequency~age, ...)

Documentation elsewhere describes one method for doing this in Stata based
on Sigelman and Zeng: http://polisci.osu.edu/prl/Selection%20Models.pdf -
see page 16.

I'd like to replicate this in r, but wanted to check I'm not reinventing the
wheel, before doing so.

Any help is much appreciated.

Best regards

Mark

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