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From |
"Clyde Schechter" <clyde.schechter@einstein.yu.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: compare effect size between dummys and metrics variables in logistic |

Date |
Tue, 28 Sep 2010 08:22:32 -0700 |

Although I think these situations are very rare, I have seen at least one instance where a sensible comparison between the coefficient of a dummy and the coefficient of a metric variable was done. The context was a linear regression rather than a logistic one, but the same logic could apply to a dichotomous outcome. I saw this a long time ago (it was not my work), my memory of it is hazy, and I cannot find the reference right now. But the gist of it was that the unit of analysis was the county or some other health-jurisdiction, the dependent variable was the infant mortality rate (or, probably, the log thereof), and the two predictors of interest were a dummy variable indicating whether the county had implemented some particular policy, and calendar year. The inclusion of calendar year was to capture the effect of a long-standing secular decline in infant mortality rates. In their discussion of results, the authors remarked that the coefficient of the dummy variable was approximately twice the coefficient of time--and they even did a test of that hypothesis. From that they concluded that implementation of the policy in question had an impact roughly equivalent to leaping forward two years in time with respect to progress in reducing infant mortality. I wish I could remember more details and find the reference. Obviously that conclusion is also contingent on the model's being properly specified, and substantive assumptions supporting causality. But I think it illustrates a (possibly) sensible comparison between the coefficient of a dummy and the coefficient of an interval-level variable. Clyde Schechter, MA MD Associate Professor of Family & Social Medicine Albert Einstein College of Medicine Bronx, NY, USA Please note new e-mail address: clyde.schechter@einstein.yu.edu * * 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/

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