# AW: AW: st: logit with interaction and transformation

 From "Pabst Alexander" To Subject AW: AW: st: logit with interaction and transformation Date Mon, 3 Aug 2009 13:52:40 +0200

```Great. This is a step closer to the solution.

But I actually want the odds ratios of the (ln transformed) independent variable at different values of the (non-transformed) moderator, i.e. just the other way around.
To stay at your example, that would mean want I want the odds ratios of grade when at different values of wage. Would it then read like this below?
But this yields big ORs, so I assume there`s still a mistake in!?

Alex

*--------------------- begin example ------------------

logit union lngrade wage wageXlngrade married never_married, or

sum wage if e(sample)
global m = r(mean)
global sd = r(sd)

nlcom (mean_minus_1sd:                             	///
exp( (exp(_b[lngrade])) + 			///
(\$m-\$sd)*_b[wageXlngrade] ) )   	///
(mean:                                       	///
exp( (exp(_b[lngrade])) +				///
(\$m)*_b[wageXlngrade] ) )        	///
(mean_plus_1sd:                              	///
exp( (exp(_b[lngrade])) + 			///
*--------------------- end example --------------------

-----Ursprüngliche Nachricht-----
Von: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Maarten buis
Gesendet: Montag, 3. August 2009 13:03
An: statalist@hsphsun2.harvard.edu
Betreff: Re: AW: st: logit with interaction and transformation

--- On Mon, 3/8/09, Pabst Alexander wrote:
> But just for the case: would it be correct to calculate
> either
> Y= X1 + (ln)X2 + X1*(ln)X2
> sum X1
> global m  = r(mean)
> global sd = r(sd)
>
>     (1) nlcom exp(x2) + (\$m+\$sd)*X2*X1
> or    (2) nlcom exp(x2) +
> exp((\$m+\$sd)*X2*X1)
>
> Or would I have to manage this somehow in terms of marginal
> effects, e.g.
> mfx, eydx at(X1=\$m)?

None of these would be correct. Apparently (in terms of the
example below) you want the odds ratios of south when at
different values of grade. Below I picked the numbers
mean grade - 1 sd, mean grade, and mean + 1 sd. Notice that
I used the mean and standard deviation of grade and only
later transformed it into ln(grade), as this way your
interpretation will accept the unit of measurement of grade

*--------------------- begin example ------------------
sysuse nlsw88, clear
married never_married, or

sum grade if e(sample)
local m = r(mean)
local sd = r(sd)

nlcom (mean_minus_1sd:                             ///
exp( _b[south] +                         ///
ln(`m'-`sd')*_b[southXlngrade] ) )   ///
(mean:                                       ///
exp( _b[south] +                         ///
ln(`m')*_b[southXlngrade] ) )        ///
(mean_plus_1sd:                              ///
exp( _b[south] +                         ///

*--------------------- end example --------------------

Hope this helps,
Maarten

-----------------------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://home.fsw.vu.nl/m.buis/
-----------------------------------------

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