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st: RE: Code and info for log-transformation


From   "Newson, Roger B" <r.newson@imperial.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Code and info for log-transformation
Date   Sun, 18 Nov 2007 14:15:46 -0000

A possible link is the Stata Tip of Newson (2003), which describes how
to calculate confidence intervals for geometric means and their ratios
using -regress- with the -eform()- option. A post-publication update can
be downloaded from
http://www.imperial.ac.uk/nhli/r.newson/papers.htm

However, as Austin says, you need not transform y just because it is
skewed. If you are more interested in median differences than in
geometric mean ratios, then you can use the -cendif- or -censlope-
commands to calculate confidence intervals for median differences and
slopes, for data which may be skewed or otherwise non-Normal. The
-cendif- and -censlope- commands are part of the -somersd- package,
which you can download from SSC, and which calculates confidence
intervals for a wide range of rank statistics.

I hope this helps


References

Newson R. Stata tip 1: The eform() option of regress. The Stata Journal
2003; 3(4): 445. Download post-publication update from
http://www.imperial.ac.uk/nhli/r.newson/papers.htm

Roger Newson
Lecturer in Medical Statistics
Respiratory Epidemiology and Public Health Group
National Heart and Lung Institute
Imperial College London
Royal Brompton campus
Room 33, Emmanuel Kaye Building
1B Manresa Road
London SW3 6LR
UNITED KINGDOM
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Email: r.newson@imperial.ac.uk 
Web page: www.imperial.ac.uk/nhli/r.newson/
Departmental Web page:
http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/pop
genetics/reph/

Opinions expressed are those of the author, not of the institution.

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Ziad
El-Khatib
Sent: 16 November 2007 22:50
To: statalist@hsphsun2.harvard.edu
Subject: st: Code and info for log-transformation

Dear STATA lister
i am trying to find more info how to write command for
log-transformation because i have skewed data?

Or if you have any link to recommend to see?


Thank you in advance and best regards
ziad
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