Hello, I have interval censored data, censored between (0, 100). I used the tobit function in the AER package which in turn backs on survreg. Actually I'm struggling with the distribution. Data is asymmetrically distributed, so first choice would be a Weibull distribution. Unfortunately the Weibull doesn't allow for zero values in time data, as it requires x > 0. So I tried the exponential distribution that allows x to be >= 0 and the log-normal that sets x <= 0 to 0. Still I get the same error:
" Fehler in survreg(formula = Surv(ifelse(A16_1_1 >= 100, 100, ifelse(A16_1_1 <= : Invalid survival times for this distribution " The only distributions that seem to work are gaussian and logistic, but they don't really fit the data. I searched for this problem in the archive and found a suggestion by Terry Therneau to set all 0 to NA, applying Weibull afterwards. But this solution is not very satisfying as it eliminates the left censored data from the dataset. So I have three questions: 1. Does anybody know why the lognormal and exponential distribution don't work in survreg? 2. What else could I do to find a distribution that fits the data well? 3. What about the non-parametric approach in survfit(), could that be a solution? I hope my question aren't too stupid, as I'm not a big statistician. Regards, Geraldine ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
