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From |
Steven Samuels <sjsamuels@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: Power calculation for competing risks regression |

Date |
Mon, 22 Aug 2011 18:20:54 -0400 |

Actually, the code can be shortened. Steve *************CODE BEGINS************* webuse hypoxia, clear stset dftime, failure(failtype==1) stcrreg ifp tumsize, compete(failtype==2) stcrreg, noshr capture net install st0074.pkg, replace powercal pow1, nunit(e(N_fail)) /// delta(log(1.06)) sdinf(sqrt(e(N_fail))*_se[ifp]) alpha(.05) list pow1 in 1 **************CODE ENDS************** I agree with Rich. Post-Hoc power calculations are too late: if your study had found a p-value of 0.05 exactly, for example, the post-hoc power to detect the observed effect would have been 50%. But arguing with reviewers who don't know better is fruitless. The following is approximate. Simulation would be better, but for your purpose, I don't think it matters. Steve *************CODE BEGINS************* webuse hypoxia, clear stset dftime, failure(failtype==1) stcrreg ifp tumsize, compete(failtype==2) stcrreg, noshr di _se[ifp] scalar nfail = e(N_fail) scalar sd = sqrt(e(N_fail))*_se[ifp] scalar list sd scalar log_eff1 = log(1.06) // HR = 1.06 capture net install st0074.pkg, replace // Roger Newson's -powercal- package powercal pow1, nunit(nfail) /// delta(log_eff1) sdinf(sd) alpha(.05) list pow1 in 1 **************CODE ENDS************** On Aug 22, 2011, at 11:36 AM, Richard Goldstein wrote: I disagree that a post-hoc power analysis is ever a good idea (see http://www.stat.uiowa.edu/~rlenth/Power/ for more on this) instead I recommend looking at the CI's and seeing whether anything of substantive interest is included in the CI; if yes, you have insufficient power; if no, I see no problem Rich On 8/22/11 11:29 AM, Hackney, David wrote: > Hello all, > > Does anyone have advice on power (or sample size) calculations for competing risks (stcrreg) in Stata? We did a competing risks regression and found that the HR for the variable of interest was non-significant and the reviewers (reasonably) asked for a post-hoc power analysis to provide support for our conclusion. There is no competing risk model specific power calculation which appears to be available, though I didn't know if one of the other power commands could be modified to accommodate competing events, or if a user-written program existed (I couldn't find one with the search function). Thanks. > > David Hackney > > > > PS. My apologies if I have sent this multiple times, I'm just not sure if I have done it correctly. Thanks. > > > David N Hackney MD, MS > Assistant Professor > Division of Maternal-Fetal Medicine > Department of Obstetrics and Gynecology > University of Rochester Medical Center > Phone (admin assistant): 585-275-7480 > Fax: 585-256-1416 > david_hackney@URMC.rochester.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/ * * 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**:**st: RE: Power calculation for competing risks regression***From:*"Hackney, David" <David_Hackney@urmc.rochester.edu>

**Re: st: RE: Power calculation for competing risks regression***From:*Richard Goldstein <richgold@ix.netcom.com>

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