On Nov 13, 2009, at 3:17 AM, carol white wrote:
Hi,
Is it normal to get intercept in the list of covariates in the
output of survreg function with standard error, z, p.value etc? Does
it mean that intercept was fitted with the covariates? Does Value
column represent coefficients or some thing else?
Don't you need a baseline scale parameter for the Weibull function?
You didn't offer the structure of your dataframe, but if it is the
"standard" ovarian set, then the rx coef is just the difference
between the scale parameter of rx=2 from that of rx=1, and similarly
for ecog.ps. You would not have an estimate for rx=1 and ecog.ps=1 if
you were not given the Intercept coef.
In the future it would be good manners to indicate what grad school
you are taking classes at.
--
David
Regards,
-------------------------------------------------
tmp = survreg(Surv(futime, fustat) ~ ecog.ps + rx, ovarian,
dist='weibull',scale=1)
summary(tmp)
Call:
survreg(formula = Surv(futime, fustat) ~ ecog.ps + rx, data = ovarian,
dist = "weibull", scale = 1)
Value Std. Error z p
(Intercept) 6.962 1.322 5.267 1.39e-07
ecog.ps -0.433 0.587 -0.738 4.61e-01
rx 0.582 0.587 0.991 3.22e-01
Scale fixed at 1
Weibull distribution
Loglik(model)= -97.2 Loglik(intercept only)= -98
Chisq= 1.67 on 2 degrees of freedom, p= 0.43
Number of Newton-Raphson Iterations: 4
n= 26
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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and provide commented, minimal, self-contained, reproducible code.
