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st: R: Log of nonpositive numbers


From   "Carlo Lazzaro" <carlo.lazzaro@tin.it>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: R: Log of nonpositive numbers
Date   Sat, 29 Mar 2008 09:45:56 +0100

Dear Ucb_gal,

a tempative answer might be to add a little constant to your zeros, in order
to make natural log transformation feasible. However, this trick will give
you back <0 values. 

Kind Regards,

Carlo

-----Messaggio originale-----
Da: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di ucb_gal
Inviato: sabato 29 marzo 2008 6.57
A: statalist@hsphsun2.harvard.edu
Oggetto: st: Log of nonpositive numbers

Hi,

I've seen this question asked a few other times, but I'm still a little
unclear on what the considerations are in thinking this through.

I'm running logistic regressions with the log of income and wealth as
independent variables.  I've seen this done often enough that I didn't
really think twice about it.  But then I realized that while I don't have a
ton of cases with exact 0 values in either variable, I do have a number of
cases with negative wealth.  And all of these show up as missing now.

Am I mistaken in thinking that I've seen studies that use the log of income
as predictors??

Thanks!




 
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