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st: RE: nl-function log4-formula


From   Nick Cox <n.j.cox@durham.ac.uk>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: nl-function log4-formula
Date   Wed, 16 Nov 2011 10:36:08 +0000

I don't know, but tucking the -if- condition inside the parentheses looks a bit odd. Try moving it outside. 

-nl- is a command, not a function. 

Nick 
n.j.cox@durham.ac.uk 

Jennyfer Wolf

I am working with the nl-function and with the logistic function model log 4.
Could somebody please explain me why I do not get the same outout if I type:

1. nl log4: VAR1 VAR2 if VAR3=="xxx"

and

2. nl(VAR1={b0}+{b1}/(1+exp(-{b2}*(VAR2-{b3}))) if VAR3=="xxx")

Actually 1. should just be an abbreviation of 2.?
If I run command 1, I get estimates for b0, b1, b2, b3, if I run
command 2 I only get an estimate for b0 and b1-b3 are 0.

Could somebody explain how to write the formula "in full" (like in
2.), to get the same results as in the first formula.


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