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RE: st: FW: Marginal effects for the two-part model

From   "Michael Palmer" <>
To   <>
Subject   RE: st: FW: Marginal effects for the two-part model
Date   Thu, 3 Feb 2011 16:49:08 +1100

Thanks for the clarification! Mills' not Mill's - mental note. There
seems to be some confusion on the computation of marginal effects for
the TPM I described as some authors still suggest combined marginal
effects. This paper for example distinguishes the Heckit model and its
inverse Mills' ratio from the TPM yet presents combined marginal effect
calculations in both instances:

Cheers, Michael  

Michael Palmer
PhD Candidate 
National Centre for Epidemiology and Population Health 
The Australian National University 
Ph. 6125 0538
M. 0437 867 940

-----Original Message-----
[] On Behalf Of Maarten buis
Sent: Thursday, 3 February 2011 2:19 AM
Subject: RE: st: FW: Marginal effects for the two-part model

--- On Wed, 2/2/11, Maarten buis wrote:
> The difference between that and your two-part model is that in that 
> model the dependence is included by deriving the inverse Mill's ratio 
> from the selection model, add it to the OLS model, and adjust the 
> standard errors.

Nick is in a pedantic mood today(*). He correctly pointed out to me
privately that it is Mills' ratio and not Mill's ratio. (And the moment
he told me, I remembered that he made that point before, and at that
time I made a mental note not to make that mistake...

-- Maarten

(*) but see the entry on pedantry in this glossary:

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen


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