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From |
"FEIVESON, ALAN H. (AL) (JSC-SK) (NASA)" <alan.h.feiveson@nasa.gov> |

To |
"'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Log transform of skewed data |

Date |
Wed, 2 Jun 2004 14:18:47 -0500 |

Stephen - It sounds as if you really have a mixed discrete-continuous distribution with an atom at zero. I don't see why the distribution would bimodal, however. Nevertheless, you can't simply take logs if zeros are in your data. Perhaps you need something like a -heckman- regression model where a "zero" is considered a non-response. Then you could apply this model to logs of the non-zero values. Al Feiveson -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Stephen Soldz Sent: Wednesday, June 02, 2004 1:53 PM To: statalist@hsphsun2.harvard.edu Subject: st: Log transform of skewed data 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 * * 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/ * * 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/

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