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From |
Allen Buxton <ABUXTON@childrensoncologygroup.org> |

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

Subject |
st: RE: p-values for K-M point survival estimates using sts list |

Date |
Wed, 25 Aug 2010 11:39:04 -0700 |

I have used a z-test for two samples with known mean and std deviation to match the output of a program called Epilog. This is to state that the KM estimate is the mean and the associated standard error are known. The confidence intervals are better. Here is the form: capture program drop epiwald program define epiwald version 9.2 args m1 s1 m2 s2 local d = abs(`m2' - `m1') local s = sqrt(`s1'^2 + `s2'^2) local z = `d'/`s' local p = 2*(1-norm(`z')) local p1 = 1*(1-norm(`z')) foreach Xval in m1 s1 m2 s2 d s z p p1 { local txt = `"``Xval''"' local `Xval'=string(`txt',"%6.4f") } di `"mu1=`m1', mu2=`m2', std1=`s1', std2=`s2'"' di `"difference=`d', std=`s'"' di `"z-value=`z'"' di `"p-value=`p'"' di `"p-1side=`p1'"' di `""' end *example . epiwald 0.5833 0.1423 0.1538 0.1001 mu1=0.5833, mu2=0.1538, std1=0.1423, std2=0.1001 difference=0.4295, std=0.1740 z-value=2.4687 p-value=0.0136 p-1side=0.0068 -Allen Buxton -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Bell, Cynthia Sent: Wednesday, August 25, 2010 8:42 AM To: statalist@hsphsun2.harvard.edu Subject: st: p-values for K-M point survival estimates using sts list The "sts list" command provides point estimates, std errors, and confidence intervals at exact times during my observation period. I prefer confidence intervals to compare, say, 10-year survival estimates between groups but a journal requested p-values comparing group point estimates at specific time points. Is this possible in Stata? If not, it shouldn't be complicated to compute a p-value given a distribution for the K-M survival point estimate and the standard error, right? Thanks very much, Cynthia Bell Division of Pediatric Nephrology and Hypertension University of Texas-Houston, Medical School * * 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: p-values for K-M point survival estimates using sts list***From:*"Bell, Cynthia" <Cynthia.Bell@uth.tmc.edu>

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