[R] survival function with a Weibull dist

From: Anaid Diaz <syadp_at_yahoo.com.mx>
Date: Thu 21 Sep 2006 - 10:48:12 GMT


Hi
I am using R to fit a survival function to my data (with a weibull distribution).

Data: Survival of individuals in relation to 4 treatments ('a','b','c','g')

syntax:
---- > survreg(Surv(date2)~males2, dist='weibull')

But I have some problems interpreting the outcome and getting the parameters for each curve.

I know from Venables & Ripley (2002) that the parameters of this function should be two:

lambda = z (presumably "Value" in R for each treatment)
alpha = k (scale in R)

Survival function (S):

S(t)= exp-(zt)^k

I don't quite understand how to use the intercept. First I thought adding it to each other treatment value, for example:

Survival Males2a (t) = exp – ((intercept + 0) * t) ^ k Survival Males2b (t) = exp – ((intercept + zb)* t) ^ k

But the curves I get using this interpretation are not similar to my data

Does anyone use this function and could help me to interpret the results?

many thanks

Anaid



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