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From |
Tim Evans <Tim.Evans@wmciu.nhs.uk> |

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

Subject |
st: RE: time varying covariate Cox regression |

Date |
Thu, 9 Feb 2012 17:12:20 +0000 |

Thanks for the response Jan. I'm confused though because recoding using your example below seems to me to put worst and best prognosis values together i.e. recode TCATOG2_1 (1=0) (2=1) (3=0) What I need is to say that 1 is the base, and compare 2, and then separately 3 against the base. I can only see that I am combining two groups (in your example mid and worst prognosis and good and worst prognosis) together as the base. Perhaps I am missing something? Best wishes Tim -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Reinhardt Jan Dietrich Sent: 08 February 2012 17:34 To: statalist@hsphsun2.harvard.edu Subject: st: AW: time varying covariate Cox regression The easiest is to recode your time varying covariate into two dummies: level1 and level2 (level 3 is the reference then) E.g. Gen TCATOG2_1 = TCATOG2 RECODE TCATOG2_1 (1=1) (2=0) (3=0) Gen TCATOG2_2 = TCATOG2 RECODE TCATOG2_1 (1=0) (2=1) (3=0) Then use both dummies instead of i.TCATOG2 ... Jan ________________________________________ Von: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu]" im Auftrag von "Tim Evans [Tim.Evans@wmciu.nhs.uk] Gesendet: Mittwoch, 8. Februar 2012 18:24 An: 'statalist@hsphsun2.harvard.edu' Betreff: st: time varying covariate Cox regression I have a time varying covariate that I am using in a Cox regression which relates to stage at diagnosis for a particular cancer type. The accepted view is that later stage tumours will have higher hazard ratios. However I have a variable with three levels that purports to suggest that later stage tumours will actually reduce the hazard ratio. I think this is being confounded by a larger number of earlier stage tumours. What I would like to know is how do I treat a categorical variable that varies with time since I don't appear to be able to use the i. prefix when using tvc. My code is thus: foreach var of varlist DELAY_* TDELAY_1 { stcox `var' age i.ttype i.grade SEX2, tvc(TCATOG2 sizegrp) } Output: ------------------------------------------------------------------------------ _t | Haz. Ratio Std. Err. z P>|z| [95% Conf. Interval] -------------+---------------------------------------------------------------- main | DELAY_1_NEW | 1.157908 .0788916 2.15 0.031 1.013162 1.323332 age | 1.053658 .0038644 14.25 0.000 1.046111 1.06126 | ttype | 2 | 2.079459 .2228057 6.83 0.000 1.685573 2.565389 3 | 1.635624 .1590821 5.06 0.000 1.351745 1.979119 | grade | 2 | 1.23092 .104672 2.44 0.015 1.041952 1.454161 3 | 2.162566 .2359455 7.07 0.000 1.746222 2.678176 | SEX2 | 1.171438 .0926916 2.00 0.046 1.003152 1.367955 -------------+---------------------------------------------------------------- tvc | TCATOG2 | .956024 .0074053 -5.81 0.000 .9416196 .9706488 sizegrp | 1.001568 .0038096 0.41 0.680 .9941292 1.009063 ------------------------------------------------------------------------------

**References**:**st: How to drop low frequency patterns from panel data***From:*Kim Peeters <kimpeeters84@yahoo.com>

**Re: st: How to drop low frequency patterns from panel data***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: How to drop low frequency patterns from panel data***From:*Kim Peeters <kimpeeters84@yahoo.com>

**Re: st: How to drop low frequency patterns from panel data***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: How to drop low frequency patterns from panel data***From:*Kim Peeters <kimpeeters84@yahoo.com>

**Re: st: How to drop low frequency patterns from panel data***From:*Nick Cox <njcoxstata@gmail.com>

**st: Rehape help***From:*Tim Evans <Tim.Evans@wmciu.nhs.uk>

**st: Concatenating two numerical variables with labels***From:*Tim Evans <Tim.Evans@wmciu.nhs.uk>

**Re: st: Concatenating two numerical variables with labels***From:*Maarten Buis <maartenlbuis@gmail.com>

**st: time varying covariate Cox regression***From:*Tim Evans <Tim.Evans@wmciu.nhs.uk>

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