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From |
Richard Williams <Richard.A.Williams.5@ND.edu> |

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

Subject |
Re: st: Odds ratio |

Date |
Fri, 09 Apr 2010 08:12:29 -0400 |

At 02:14 AM 4/9/2010, Maarten buis wrote:

--- On Fri, 9/4/10, Rosie Chen wrote: > I am doing HLM analysis, so it is impossible to use the Stata > syntaxt to calculate the predicted probability. So I will > just do the calculation by myself in excel. Here is what I > plan to do: I will calculate log-odds and then convert > them into predicted probabilities for individuals with > characteristics that I am interested in so as to demonstrate > the magnitude of the effect for a specific variable. Sorry for being blunt but that is a very bad idea. There are very good reasons why Stata isn't giving you those probabilities directly: These multilevel models take into account group level variation, while your approach doesn't.

> For example, in order to explain the gender difference in the > probability of an outcome, I will compute the difference in > the predicted probability between females and males The key issue with odds ratios is that I would like to have the baseline odds present, to help me interpret the odds ratio (which in a sense helps to bridge the gap between absolute and relative effects). The problem is that by default Stata suppresses those. The trick is to add a variable baseline, which is always one, and add the -noconstant- option. This trick is discussed in the paper I refered to before, and I learned it from: Roger Newson (2003), Stata tip 1: The eform() option of regress. The Stata Journal, 3(4): 445. <http://www.stata-journal.com/article.html?article=st0054>

I am slowely getting used to odds, so the distinction between odds and probabilities doesn't bother me any more: You can quantify the likelihood of an event by computing the expected number of success per 100 trials (100*probability) or by the expected number of success per failure (the odds). Just don't mix the two up, as sometimes happens when people try to interpret odds ratios as risk ratios.

------------------------------------------- Richard Williams, Notre Dame Dept of Sociology OFFICE: (574)631-6668, (574)631-6463 HOME: (574)289-5227 EMAIL: Richard.A.Williams.5@ND.Edu WWW: http://www.nd.edu/~rwilliam * * 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/

**Follow-Ups**:**Re: st: Odds ratio***From:*Rosie Chen <jiarongchen2002@yahoo.com>

**Re: st: Odds ratio***From:*Maarten buis <maartenbuis@yahoo.co.uk>

**References**:**Re: st: Odds ratio***From:*Rosie Chen <jiarongchen2002@yahoo.com>

**Re: st: Odds ratio***From:*Maarten buis <maartenbuis@yahoo.co.uk>

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