As has been answered several times on rhelp ... the baseline hazard is
for a case with the "mean value". It's not a meaningful case with
all
factor variables. There can be no cases where fidelity>3 has a
fractional value. You should be using predict() and survfit() to
display estimates for particular meaningful cases. You might want to
use a different rhs formula as well because the one offered omits the
main effects. Choosing ~bucket*factor(fidelity > 3) would include
those terms.
--
David.
On May 1, 2012, at 8:37 PM, Georges Dupret wrote:
> Hi,
>
> In the following results I interpret exp(coef) as the factor that
> multiplies
> the base hazard rate if the corresponding variable is TRUE. For
> example,
> when the bucket is ks008 and fidelity <= 3, then the rate, compared
> to the
> base rate h_0(t), is h(t) = 0.200 h_0(t). My question is then, to
> what case
> does the base hazard rate correspond to? I would expect the
> reference to be
> the first factor value, i.e. bucket jpc001 with fidelity <= 3, but its
> exp(coef) is not one. I verified the contrasts, and the row
> corresponding to
> the first factor value is zero everywhere; moreover, I didn't change
> the
> default, so a bad setting of the contrasts doesn't seem to be the
> issue.
>
> Best,
>
> ge
>
> Call:
> coxph(formula = Surv(time, event = (censored => FALSE)) ~
bucket:factor(fidelity > 3), data = week.15)
>
>
> coef exp(coef) se(coef)
> z p
> bucketjpc001:factor(fidelity > 3)FALSE -1.606 0.201 0.00624
> -257.5 0
> bucketks006:factor(fidelity > 3)FALSE -1.613 0.199 0.00627
> -257.5 0
> bucketks007:factor(fidelity > 3)FALSE -1.620 0.198 0.00626
> -258.8 0
> bucketks008:factor(fidelity > 3)FALSE -1.611 0.200 0.00625
> -257.6 0
> bucketks009:factor(fidelity > 3)FALSE -1.620 0.198 0.00626
> -258.9 0
> bucketks010:factor(fidelity > 3)FALSE -1.619 0.198 0.00626
> -258.6 0
> bucketjpc001:factor(fidelity > 3)TRUE -0.156 0.856 0.00596
> -26.2 0
> bucketks006:factor(fidelity > 3)TRUE -0.171 0.842 0.00600
> -28.6 0
> bucketks007:factor(fidelity > 3)TRUE -0.168 0.845 0.00602
> -28.0 0
> bucketks008:factor(fidelity > 3)TRUE -0.167 0.846 0.00600
> -27.8 0
> bucketks009:factor(fidelity > 3)TRUE -0.170 0.844 0.00599
> -28.4 0
> bucketks010:factor(fidelity > 3)TRUE NA NA 0.00000
> NA NA
>
> Likelihood ratio test=294562 on 11 df, p=0 n= 1173838, number of
> events> 629383
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/coxph-reference-hazard-rate-tp4602092.html
> Sent from the R help mailing list archive at Nabble.com.
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT