[R] survreg function in survival package

[David Winsemius]

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