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From |
Hitesh Chandwani <hchandwani.stata@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Interpreting coefficients for a gamma regression with log link (Stata 11) |

Date |
Tue, 20 Sep 2011 08:37:19 -0500 |

Thank you Thomas for the comments and help. I really appreciate it! -Hitesh On Mon, Sep 19, 2011 at 10:17 AM, Weichle, Thomas <Thomas.Weichle@va.gov> wrote: > Hi Hitesh, > As you know may know, the output being displayed is different depending > on whether you specify the eform option or not. The resulting model is > the same but the interpretation of the coefficients is slightly > different. Suppose x is a 1/0 variable. Then, b = > ln(E(y|x=1))/ln(E(y|x=0)) is the unexponentiated coefficient for x and > e(b) = e^[ln(E(y|x=1))/ln(E(y|x=0))] = e^[ln(E(y|x=1))]/[e^ln(E(y|x=0))] > = E(y|x=1)/E(y|x=0) is the exponentiated coefficient for x. When > dealing with cost as an outcome, Blough (2000) states that the ratio > directly interpreted from the exposure variable may be preferable to > point estimates (unexponentiated coefficient). > > Returning to your specific questions: > 1) You are correct in stating that the exponentiated coefficient of > 1.031383 represents the arithmetic mean ratio in the dependent variable > between HIV+ and HIV- patients [specifically mean(hiv=1)/mean(hiv=0)]. > > 2) Since 'insurance_3' is the reference category, the exponentiated > coefficient for 'insurance_1' is interpreted as the following ratio: > [mean(insurance_1)/mean(insurance_3)]. > > Tom Weichle > Math Statistician > Center for Management of Complex Chronic Care (CMC3) > Hines VA Hospital, Bldg 1, C202 > 708-202-8387 ext. 24261 > Thomas.Weichle@va.gov > > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > -- Hitesh S. Chandwani University of Texas at Austin * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**Re: st: Interpreting coefficients for a gamma regression with log link (Stata 11)***From:*"Weichle, Thomas" <Thomas.Weichle@va.gov>

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