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I'm using survreg function in R and

survreg(Surv(time,status) ~ variables, rain,dist="lognormal")

gives me Invalid survival times for this distribution. The name of variable is indeed time and it doesn't contain negative values.

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1 Answer 1

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The survreg function in R does not allow time = 0. This is because for several of the distributions, including the lognormal distribution, having events occur at time = 0 will result in an undefined estimator.

You can think that having time = 0 for a lognormal would be similar to having y = -Inf for a normal distribution.

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  • $\begingroup$ Thanks for your answer. I have a lot of zeros in my data. Does this mean that I should remove zeros (or change them to a very small value like 0.00001) or I can use a different distribution? $\endgroup$
    – Erin
    Oct 10, 2015 at 20:45
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    $\begingroup$ That's a little tricky. The reason for this is it will have a large impact if you switch 0's for 0.1 or 0.000001. To properly answer your question, it helps to know why you have some many zeros. $\endgroup$
    – Cliff AB
    Oct 10, 2015 at 22:23

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