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# Re: st: RE: nl-function log4-formula

 From Jennyfer Wolf To statalist@hsphsun2.harvard.edu Subject Re: st: RE: nl-function log4-formula Date Wed, 16 Nov 2011 12:23:08 +0100

```Dear Nick,

thanks for your answer.
I tried with the parantheses outside:

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

It does not change anything. Still I don't get same reults as with
log4 and only an estimate for b0.
Would you have another idea?

Thank you!
Jennyfer

2011/11/16 Nick Cox <n.j.cox@durham.ac.uk>:
> 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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```

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