It would seem to me that your problem is in your data. For survreg, you have
to have positive durations, and if your data have y>=-5 as seen in
>Error in survreg(Surv(y, y >= -5, type = "left") ~ x + :
> Invalid survival times for this distribution
>In addition: Warning messages:
>1: In log(dlist$dtrans(Y[exactsurv, 1])) : NaNs produced
>2: In log(y) : NaNs produced
then you have negative durations in the data. I would suggest truncating your
data at y>0, as that would avoid taking natural logs of negative numbers.
Corey Sparks
Corey S. Sparks, Ph.D.
Assistant Professor
Department of Demography and Organization Studies
University of Texas San Antonio
One UTSA Circle
San Antonio, TX 78249
email:[EMAIL PROTECTED]
Date: Fri, 25 Apr 2008 10:02:21 -0700 (PDT)
From: Abdus Sattar <[EMAIL PROTECTED]>
Subject: Re: [R] Use of survreg.distributions
To: Terry Therneau <[EMAIL PROTECTED]>
Cc: r-help@R-project.org
Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain
Hello Dr. Therneau:
Thank you for your response. Let me explain to you want I want. My y
variable(time) is normal and would like to fit the model on logarithmic
transformation of y (log(y)). I tried to run codes according to your suggestion:
tfit=survreg(Surv(y, y>=-5, type="left")~x + cluster(id), dist="lognormal",
data=y.data, scale=0, weights=w)
The following error message is giving:
Error in survreg(Surv(y, y >= -5, type = "left") ~ x + :
Invalid survival times for this distribution
In addition: Warning messages:
1: In log(dlist$dtrans(Y[exactsurv, 1])) : NaNs produced
2: In log(y) : NaNs produced
Note, the data file y.data does not contain any missing data! Do you know why
it is giving me such an error message please?
Thank you again for your helpful comment/suggestion.
Best Regards,
Abdus Sattar
[EMAIL PROTECTED]
----- Original Message ----
From: Terry Therneau <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Cc: r-help@R-project.org
Sent: Friday, April 25, 2008 8:46:45 AM
Subject: Re: [R] Use of survreg.distributions
--begin included message ---
I am using survreg(Surv()) for fitting a Tobit model of left-censored
longitudinal data. For logarithmic transformation of y data, I am trying use
survreg.distributions in the following way:
tfit=survreg(Surv(y, y>=-5, type="left")~x + cluster(id), dist="gaussian",
data=y.data, scale=0, weights=w)
my.gaussian<-survreg.distributions$gaussian
my.gaussian$name="lognormal"
my.gaussian$dist<-my.gaussian
tfit=survreg(Surv(y, y>=-5, type="left")~x + cluster(id), dist=my.gaussian,
data=y.data, scale=0, weights=w)
If I run these codes then I got the following error message,
Error in survreg(Surv(y, y >= -5, type = "left") ~ x + :
Invalid distribution object
Does anybody can help me in identifying the error(s) in these code please?
--- end include ----
Can you tell us what you are trying to do?
Your first model was a fit of y ~ x + eps, eps ~ Gaussian. If what you want
is log(y) ~ x + eps, then all that you need do is use dist="loggaussian" in the
survreg call. (Or 'lognormal'; which is the same distribution.)
Terry Therneau
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