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From |
James McJoseph <[email protected]> |

To |
[email protected] |

Subject |
Re: st: Heckprob - Why no margins in selection equation? |

Date |
Tue, 30 Nov 2010 15:35:08 +0200 |

much, thanks. On Tue, Nov 30, 2010 at 3:27 PM, Maarten buis <[email protected]> wrote: > --- On Tue, 30/11/10, James McJoseph wrote: >> Could someone enlighten me plse. I use stata 11. I >> estimated -heckprob-. I requested -margins, dydx(_all)-. >> Stata gives me margins for the obejective equation >> only. For the selection equation, it gives "missing". >> Why? > > A marginal effect is the first derivative of some > outcome measure with respect to explanatory variables. > In models like -heckprob- there are multiple outcome > measures posible: the marginal probability of success, > the probability of success given that someone is selected, > the probability of being selected, etc. So -margins- > needs to know what outcome measure you mean. By default, > it looks at the predict option of your command, in this > case -heckprob-, and looks at the default prediction and > assumes that that is what you want. You can (and should) > find out yourself what that default is by typing in Stata > -help heckprob postestimation-. Then you will find that > the default prediction of -heckprob- is the marginal > probability of succes, so it makes no sense to have that > marginal effect type for the selection equation and Stata > wisely keeps them missing. You can change your outcome > measure by specifying the -predict- option in -margins-. > > Hope this helps, > Maarten > > -------------------------- > Maarten L. Buis > Institut fuer Soziologie > Universitaet Tuebingen > Wilhelmstrasse 36 > 72074 Tuebingen > Germany > > http://www.maartenbuis.nl > -------------------------- > > > > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Heckprob - Why no margins in selection equation?***From:*James McJoseph <[email protected]>

**Re: st: Heckprob - Why no margins in selection equation?***From:*Maarten buis <[email protected]>

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