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Re: st: xtgee for skewed data


From   José Maria Pacheco de Souza <jmpsouza@usp.br>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: xtgee for skewed data
Date   Thu, 25 Aug 2011 11:12:18 -0300

Em 25/08/2011 08:15, Nick Cox escreveu:
The discussion started by William Gould at

http://blog.stata.com/2011/08/22/use-poisson-rather-than-regress-tell-a-friend/

seems relevant. You have a massive spike in the distribution. No
transformation will much affect that, as by Murphy's theorem a spike
maps to a spike, and in any case there would be the usual argument
about what to do with zeros. However, (importantly different here)
.....

Dear Statalisters:
I am not sure whether I can include this question in the thread above, but the subjet is related. If the interest is to run a linear regression of a continuous variable as the response, say level of beta carothen, and for very small values the results are zero because the equipment can only show values equal or greater than .04, the use of -tobit- can be an statistical alternative?
Let´s assume there is no money to buy a better device.
Best regards,
josé maria
--
Jose Maria Pacheco de Souza
Professor Titular (aposentado), Colaborador Senior
Departamento de Epidemiologia/Faculdade de Saude Publica, USP
Av. Dr. Arnaldo, 715
01246-904  -  S. Paulo/SP - Brasil
fones (11)3061-7747; (11)3768-8612
www.fsp.usp.br/~jmpsouza
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