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st: RE: correcting skewness of an indep variable


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: correcting skewness of an indep variable
Date   Mon, 15 Mar 2010 16:18:28 -0000

Skewness of an independent variable (I prefer an alternative term such as 'predictor') is sometimes an inconvenience. I am not aware that symmetry of an independent variable is ever an assumption in modelling. 

In the case of logit there are plenty of situations in which response is conveniently taken to be a function of log predictor. I don't think the more complicated treatment of -lnskew0- is ever obviously essential. 

In any case, the whole terminology of a 'correction' is at best unfortunate here. 

Can you reproduce the error message below with one of Stata's standard datasets? It looks a very odd error, particularly because I don't think -lnskew0- makes any use of Stata's matrix language. Perhaps your copy of Stata is corrupted. 

. set trace on 

to see where the error comes from. 

Nick 
n.j.cox@durham.ac.uk 

Fabio Zona

When does one need to correct the skewness of an independent variable? I have a logit regression and my indep variable is strongly skewed; do I need to correct this (by using lnskew0 )??

I tried to correct my variable, but Stata gave this error message (see below); what does it mean? why it gave this message?

lnskew0 lnindepvar =  indepvar
invalid matrix stripe;
.z_
r(198);


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