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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

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

Subject |
st: RE: continuous to categorical and determination of monotonic categories |

Date |
Tue, 9 Dec 2003 18:29:29 -0000 |

I'll take the motivation here as given, although clearly a separate discussion on merits and demerits is possible. There may be formal machinery to do this, but I'd tend to proceed in an exploratory manner. One key is to look at the conditional distributions and see whether their properties change as expected. Among other tools, you could look at a bundle of cumulative distribution curves or kernel estimates of density functions. -distplot- or -qplot- from SSC have easy handles to draw graphs -by()-. Nick n.j.cox@durham.ac.uk cthompson@dfpm.utah.edu > The question that follows is part STATA and part statistical > technique. Suppose I have a continuous independent variable in > a logistic (or cox) model and I wish to reconfigure the > variable as a categorical (read ordinal) variable so that the > odds ratio (hazard ratio) will be more meaningful, but before I > categorize the variable and insert it into the model I'd like > to determine whether the categories (e.g hospital volume: low, > medium, high) are monotonic relative to the outcome (e.g. shunt > survival as measured in fractions of years) so as to establish > some justification of linearity. If "monotonicity" cannot be > determined, then I understand that indicator variables must be > created and odds ratios (hazard ratios) returned are relative > to a referent group. My question is two-fold: is this an > acceptable technique and if so, is there a straightforward and > acceptable way to proceed using 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/

**Follow-Ups**:**Re: st: RE: continuous to categorical and determination of monotonic categories***From:*Constantine Daskalakis <c_daskalakis@mail.jci.tju.edu>

**st: lizards: McCullagh & Nelder***From:*SR Millis <smillis@kmrrec.org>

**References**:**st: continuous to categorical and determination of monotonic categories***From:*cthompson@dfpm.utah.edu

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