Maartin,
Thanks for your response (my understanding = "there is a reason for
the difference" :)
What about the *bigger* question?
> > Should I care? What can be done about it? How do I interpret results?
If gender is insignificant in MLOGIT but significant in MFX (or vice
versa), which result should I scream from the rooftops?
Thanks!
David
On Wed, Mar 26, 2008 at 7:42 AM, David Zetland <[email protected]> wrote:
> Date: Tue, 25 Mar 2008 11:26:27 +0000 (GMT)
> From: Maarten buis <[email protected]>
> Subject: Re: st: mlogit and mfx -- statistical significance
>
> The reason for such a difference is that there is a subtle difference
> in what these two measures measure: The output from -mlogit- gives you
> a test whether the odds ratio (*) is significantly different from 1,
> while -mfx- gives you a change in probabilities.
>
> Say the odds ratio is 10, but the baseline odds is .0001 success for
> every failure, so we are talking about comparing a odds of .0001 with
> an odds of .001, which corresponds to a probabilities .00009999 and
> .000999, leading to a risk difference (result of -mfx-) of .00089901 .
>
> So a big sounding odds ratio of 10 can easily correspond to a very
> small sounding risk difference of .0009 . The reason is that by
> computing the ratio of odds, the baseline odds drops out, so whith odds
> ratios you only look groups are different but leave out the fact that
> those differences hardly matter if probability of success is very high
> or very low for everybody.
>
> Hope this helps,
> Maarten
>
> (*) Some disciplines don't call the parameters of -mlogit- log odds
> ratios, but they are the log of a ratio of odds, so I think the other
> disciplines are correct in refering to them as log odds ratios, for
> more on this see:
> http://www.stata.com/statalist/archive/2007-02/msg00085.html
>
> Ps. has anybody noticed that I have refrained from repeating my
> favourite feature request?
>
> - --- David Zetland <[email protected]> wrote:
>
> > Can anyone explain why some RHS vars are significant in <mlogit> but
> > not in <mfx> (and vice versa)?
> >
> > I have several RHS dummies, but the problem also shows up with
> > <margeff>
> >
> > Should I care? What can be done about it? How do I interpret results?
> >
> > I have searched the FAQs and forums and seen similar questions but no
> > answers
*
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