[R] interval-censored data in survreg()

[Jerome Asselin]

I am trying to fit a lognormal distribution on interval-censored
data. Some of my intervals have a lower bound of zero.
Unfortunately, it seems like survreg() cannot deal with lower
bounds of zero, despite the fact that plnorm(0)==0 and
pnorm(-Inf)==0 are well defined. Below is a short example to
reproduce the problem.

Does anyone know why survreg() must behave that way?
Is there an alternate solution to this problem?

Sincerely,
Jerome Asselin

library(survival)
data(ovarian)
newovarian <- ovarian

newovarian$lower59 <- newovarian$futime-59
newovarian$time59 <- Surv(newovarian$lower59,newovarian$futime,
    event=rep(3,nrow(newovarian)),type="interval")
survreg(time59~ecog.ps+rx,data=newovarian,dist="lognormal")
#THIS DOES NOT WORK BECAUSE ONE OF THE LOWER BOUNDS IS ZERO
#Error in survreg(time59 ~ ecog.ps + rx, data = newovarian,
#  dist = "lognormal") :
#        Invalid survival times for this distribution

-- 

Jerome Asselin (Jérôme)
Statistical Analyst
British Columbia Centre for Excellence in HIV/AIDS
St. Paul's Hospital
608 - 1081 Burrard Street
Vancouver, British Columbia
CANADA V6Z 1Y6

Email: jerome at hivnet.ubc.ca
Phone: 604 806-9112   Fax: 604 806-9044