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Re: st: When to use Log (1+x) Transformation?


From   "Song" <[email protected]>
To   <[email protected]>
Subject   Re: st: When to use Log (1+x) Transformation?
Date   Mon, 7 Apr 2008 00:11:24 -0500

Thank you for your suggestion. I also want to look at the possibility of using an inverse hyperbolic sine transformation since time window includes actually some negative numbers.

Reo.

----- Original Message ----- From: "Maarten buis" <[email protected]>
To: <[email protected]>
Sent: Sunday, April 06, 2008 3:00 PM
Subject: Re: st: When to use Log (1+x) Transformation?



--- 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/
-----------------------------------------


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