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st: question on -treatreg-


From   "Martin Weiss" <martin.weiss@uni-tuebingen.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: question on -treatreg-
Date   Tue, 10 Jun 2008 14:47:05 +0200

Dear Statalisters,

I am wondering how one can reconcile the predictions flowing from -treatreg-
with a dependent variable in logs or in levels. See for yourself


******************
webuse labor, clear

qui{
	g byte wc = we > 12
	la var wc "Wife attended college (assumed)"
	la def wi 0 "no college" 1 "college"
	la val wc wi


	noi ta wc

*    Obtain full ML estimates with log specification

	noi treatreg ww wa cit, treat(wc=wmed wfed)
	predict logpredpos, yctrt
	predict logpredneg, ycntrt
	
	
	*put dependent in levels
	
	g levelww=exp(ww)
	noi treatreg levelww wa cit, treat(wc=wmed wfed)


	predict levelpredpos, yctrt
	predict levelpredneg, ycntrt


	scatter logpredpos levelpredpos, nodraw name(pos, replace)
	scatter logpredneg levelpredneg, nodraw name(neg, replace)
}

gr combine pos neg, cols(1)
******************

How could one go back from logpredpos to levelpredpos? It is not as simple
as exponentiating the logpredpos, but what do you add to that?


Thanks in advance,
Martin Weiss
_________________________________________________________________

Diplom-Kaufmann Martin Weiss
Mohlstrasse 36
Room 415
72074 Tuebingen
Germany

Fon: 0049-7071-2978184

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