--- Song <[email protected]> wrote:
> I plan to estimate the following model by 3SLS (reg3).
>
> ln(Revenue in each country) = a0 + a1*time window + controls.
> ln(time window) = b0 + b1*(expected) Revenue in each country +
> controls.
>
> Time window is difference in launching time (in days) of a product
> between the US and international launch. Both revenue and time window
> are skewed, so I wanted to use log transformation. The problem is
> that time window includes a lot of zeros, so I am not sure what is
> the best method.
One transformation you can use is the cube root:
gen cr_time_widow = time_window^(1/3)
An issue you might want to look into is that a zero time may be
qualitatively different from the other values, but I don't know how to
implement such a thing for a endogenous variable, except that I
recommend that you take a very good look at the residuals.
-- Maarten
-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands
visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
___________________________________________________________
Yahoo! For Good helps you make a difference
http://uk.promotions.yahoo.com/forgood/
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
