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Re: st: Log transform of skewed data


From   Trudy Ann Cameron <cameron@uoregon.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Log transform of skewed data
Date   Wed, 02 Jun 2004 12:37:44 -0700

One would typically entertain tobit-type specifications in this context (or
their generalizations).  They allow for heaping at zero and for a skewed
distribution in the positive domain.
Trudy

At 11:53 AM 6/2/2004, you wrote:
>I have data on the "cost" (actually tranformed hours) of various types of
>caretaking for Alzheimers patients. I'm interested in a regression model to
>test treatment effects in a multisite study. As is usual for cost data, it
>is positively skewed. So, I contemplated a log transform, either through a
>direct transformation of the response, or through a log link in a glm, gee,
>or something similar. I actually am using "xt" commands to allow for
>nonindependence among caretakers treated at the same site.
>
>the problem is that the mode cost is $0, so that the distribution is
>bimodal. This, of course, remains true if I do a lof transform. Any ideas on
>how to analyze such data would be apreciated.
>
>Stephen Soldz
>Director, Center for Research, Evaluation, and Program Development
>Boston Graduate School of Psychoanalysis
>1581 Beacon St.
>Brookline, MA 02446
>ssoldz@bgsp.edu
>http://soldzresearch.com/stephensoldz
>
>
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Trudy Ann Cameron
R.F. Mikesell Professor of Environmental
            and Resource Economics
Department of Economics, 430 PLC
1285 University of Oregon
Eugene, OR  97403-1285

phone:  (541) 346-1242
FAX:     (541) 346-1243
email:    cameron@uoregon.edu


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