[FORGED] p-value=0 running log-rank test
This is a minor problem with the print method for "survdiff" objects. It
acts like it computes the p-value with
1 - pchisq( chisq, df)
instead of
pchisq( chisq, df, lower.tail = FALSE)
The former will give zero when the latter gives a number less than about
10^-16.
Most people would accept 0 instead of 10^-16, but the 6-sigma folks worry
about probabilities of 10^-10 so perhaps it is worth making the easy change.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Thu, May 18, 2017 at 10:14 PM, Rolf Turner <r.turner at auckland.ac.nz>
wrote:
This is not an R question. Your question indicates that you really need to learn some statistics. To answer the very last part:
pchisq(430,3,lower=FALSE)
[1] 7.020486e-93 And if that is not 0 to all intents and purposes, then God help us all. cheers, Rolf Turner On 19/05/17 12:48, Anne Karin da Mota Borges wrote:
Dear all, I have a question concerning the p-value. When running log-rank test I get a p-value = 0. What is it mean? Can this be true? Why aren?t there decimal points? Is there a way to find out the exact p-value? Here is the output: survdiff(Surv(tempo2,status)~tphist, data=base,rho=0)
Call:
survdiff(formula = Surv(tempo2, status) ~ tphist, data = base,
rho = 0)
N Observed Expected (O-E)^2/E (O-E)^2/V
tphist=1 513 19 40.879 11.710 9.00e+01
tphist=2 49 4 3.892 0.003 3.27e-03
tphist=3 23 9 1.686 31.717 3.29e+01
tphist=4 18 15 0.543 385.172 3.91e+02
Chisq= 430 on 3 degrees of freedom, p= 0
Thank you in advance.
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