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From |
Mark Schaffer <M.E.Schaffer@hw.ac.uk> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Interesting (?) -ml- question |

Date |
Sat, 04 Sep 2004 17:56:19 +0100 (BST) |

Dear Statalisters, and -ml- experts in particular: I am trying to write an -ml- routine and have hit a peculiar roadblock. I am an -ml- novice, so hopefully there's an easy answer. The likelihood function that I want to minimize has the form of, say, one dependent variable y and 3 independent variables w, x and z. However, of the independent variables, only x has a coefficient associated with it. The other two variables, w and z, are needed for calculating the likelihood but don't have coefficients. My question - what's the best way of passing w and z to the likelihood function? I can think of 3 ways, but all seem pretty hacky: 1. Save "w z" as a string in a global macro called, say, MyMLvars. The likelihood program mymlprog knows to look in $MyMLvars to find them. 2. In the ml model command, list w and z as additional endogenous variables, e.g., ml model d0 mymlprog (y w z = x) Then mymlprog can find w and z as $ML_y2 and $ML_y3. 3. The hackiest of all - list w and z as indep vars, but constrain the coeffs to be zero: constraint 1 w=0 constraint 2 z=0 ml model d0 mymlprog (y = x w z) Is there a better way? Or, if there isn't, which of these is to be preferred? -Mark ________________________________________________________________ DISCLAIMER: This e-mail and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom it is addressed. If you are not the intended recipient you are prohibited from using any of the information contained in this e-mail. In such a case, please destroy all copies in your possession and notify the sender by reply e-mail. Heriot Watt University does not accept liability or responsibility for changes made to this e-mail after it was sent, or for viruses transmitted through this e-mail. Opinions, comments, conclusions and other information in this e-mail that do not relate to the official business of Heriot Watt University are not endorsed by it. ________________________________________________________________ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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