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From |
Maarten buis <maartenbuis@yahoo.co.uk> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Survival analysis |

Date |
Mon, 31 Aug 2009 09:52:49 +0000 (GMT) |

----------------------------------------- Maarten L. Buis Institut fuer Soziologie Universitaet Tuebingen Wilhelmstrasse 36 72074 Tuebingen Germany http://www.maartenbuis.nl ----------------------------------------- --- moleps islon wrote: > > This is the ouput I´m getting using your approach: > > > > n=896, failures=292 > > > > stcox var,tvc(var) texp((_t>1)_t) > > > > rh > > > > var HR 0.64, p=0.005, CI 0.47-0.87 > > > > t > > var HR 1.01,p=0.001,CI 1.01-1.03 > > > > So as far as I understand this the interpretation is > > that the -var- is protective within the first 24hrs, > > but detrimental afterwards ?? --- On Mon, 31/8/09, Maarten buis wrote: > No, the coefficient in the t equation is an interaction > effect. So from t =0 to t=1 the hazard ratio increased > with 1%. So at t=0 the hazard ratio for var is > 0.64/1.01=0.62. In other words, in the first 24hrs var > was even more protective than afterwards (but only very > little, so I doubt whether that has any practical > relevance). Sorry, I did not see that you turned around the inquality sign (from < to >). So, in your case you assume that the PH assumption holds in the first 24hrs, and that afterwards the log hazard ratio changes linearly with time. So, from t=0 to t=1 the hazard ratio of var is .64, and after t=1 the hazard ratio increases by 1% every day. At t=2 the hazard ratio of var is 1.01*.64=.646, at t=3 1.01^2*.64=.653, at t=4 1.01^3*.64=.659, etc. To get the interpretation I gave in my previous post you have to replace stcox var,tvc(var) texp((_t>1)_t) with stcox var,tvc(var) texp((_t<1)_t) Hope this helps, Maarten * * 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: Survival analysis***From:*Maarten buis <maartenbuis@yahoo.co.uk>

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