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RE: st: Simple slope analysis for non-linear models


From   Ebru Ozturk <ebru_0512@hotmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Simple slope analysis for non-linear models
Date   Mon, 25 Mar 2013 13:27:21 +0300

I just have one example: Bowen (2010) TOTAL, STRUCTURAL AND SECONDARY MODERATING EFFECTS IN THE
TOBIT MODEL AND THEIR COMPUTATION USING STATA

Do you think I can follow the formulas in this paper?

----------------------------------------
> Date: Mon, 25 Mar 2013 10:30:22 +0100
> Subject: Re: st: Simple slope analysis for non-linear models
> From: maartenlbuis@gmail.com
> To: statalist@hsphsun2.harvard.edu
>
> On Sun, Mar 24, 2013 at 11:40 AM, Ebru Ozturk wrote:
> >I followed your suggestion and it seems that I want this derivative E( y |X, y ≥ 0).
>
> ok
>
> > In my model, I have one interaction term (dummy X continuous-ranges from 0 to 10) and other Xs.
>
> This is sentence full of contradicotry statements: Do you have one or
> many interaction terms? Is your key variable a single indicator
> (dummy) variable, 10 indicator variables, or continuous?
>
> >I would like to plot the values of true interaction effect and implied z-statistic value at each observation. After doing that I would like to show the value and significance of X’s marginal effect at selected values of the moderator Z (low, mean and high). I use Stata 10.
>
> There is no such thing as a "true interaction effect". I presume you
> are looking for a cross partial derivative or discrete difference
> (depending on whether your variables are continous or categorical). As
> far as I know there is no program that does this kind of computation
> for -tobit-, so you'll need the general purpose commands -predictnl-
> and -adjust- for that in Stata 10. So, you'll need to look up the
> appropriate formulas and probably do the derivatives yourself. For
> such computations I often combine doing the derivations by hand and
> using <http://www.quickmath.com/>. After those computations you can
> feed the results to -predictnl- or -adjust-.
>
> I realize you would have liked the answer to be in the form of a
> command rather than some general tips on how to write a program that
> does what you want to do. But if no one wrote the program before, then
> that is the only answer possible. I could have written the program for
> you, but that is too big time investment on my part. I only do things
> like that if I am also interested in that problem. In this case I
> consider this way of thinking about interaction terms a dead end, so I
> am not going to invest time in it.
>
> > But the problem is in journals I use they never mention which Tobit intepretation they implement so that's why I am struggling.
>
> So they report differences/changes in predicted outcome without
> defining what the outcome is? That seems a bit problematic to me.
>
> Hope this helps,
> Maarten
>
> ---------------------------------
> Maarten L. Buis
> WZB
> Reichpietschufer 50
> 10785 Berlin
> Germany
>
> http://www.maartenbuis.nl
> ---------------------------------
>
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