Statalist


[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

st: to Marteen buis (independent variable)


From   Mohammed El Faramawi <[email protected]>
To   [email protected]
Subject   st: to Marteen buis (independent variable)
Date   Sat, 8 Mar 2008 21:49:05 -0800 (PST)

Hi Marteen,
You wrote Anyhow the real issue with transforming the
independent variables is whether the effect is linear,
or gradually slowing down (log) u-shaped, quadratic,
etc.' would you mind explaining more? especially what
do you mean by slowing down and (log)
Thank you .
--- Maarten buis <[email protected]> wrote:

> The independent variables don't need to be normally
> distributed. If you
> log transfom the variable than you think that if you
> start with a small
> dose, an increase has a much bigger effect than when
> you start with a
> larger, which may or may not make sense. Anyhow the
> real issue with
> transforming the indepedent variables is whether the
> effect is linear,
> or gradually slowing down (log) u-shaped, quadratic,
> etc. As an aside,
> if you compute percentile rank scores, you won't
> make that variable
> normal, uniformly distributed.
> 
> -- Maarten
> 
> --- Mohammed El Faramawi <[email protected]> wrote:
> > I have  questions about the independent variable
> > transformation. 
> > I have an independent variable (lead mg/dl) which
> is
> > not normally distributed. I am trying to run it in
> a
> > cox hazard model the out come is mortality. What
> > should I do with lead
> > 1) Should I log transform it? I did that but it is
> > still not normally ditributed after transformatin.
> > 2) Leave it as it is because transformation does
> not
> > change the distribution?
> > 3) categorize using quartiles or percentiles? 
> 
> 
> -----------------------------------------
> 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/
> -----------------------------------------
> 
> 
>      
>
___________________________________________________________
> 
> Rise to the challenge for Sport Relief with Yahoo!
> For Good  
> 
> 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/
> 



      ____________________________________________________________________________________
Be a better friend, newshound, and 
know-it-all with Yahoo! Mobile.  Try it now.  http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ 

*
*   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/



© Copyright 1996–2024 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index