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

 From Maarten buis To statalist@hsphsun2.harvard.edu Subject Re: AW: st: logit with interaction and transformation Date Mon, 3 Aug 2009 11:03:16 +0000 (GMT)

```--- 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
interpretation will accept the unit of measurement of grade

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

local m = r(mean)
local sd = r(sd)

nlcom (mean_minus_1sd:                             ///
exp( _b[south] +                         ///
(mean:                                       ///
exp( _b[south] +                         ///
(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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```