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From |
Antoine Terracol <Antoine.Terracol@univ-paris1.fr> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: R: st: R: Problem with Left Truncation |

Date |
Fri, 23 Oct 2009 15:53:05 +0200 |

Antoine Carlo Lazzaro wrote:

Dear Antoine, Thanks for your good point. However, I would say that if Elaine's dataset is composed of <spells short enough to have failed during the observation window> only, a selection bias issue may arise. Kind Regards, Carlo -----Messaggio originale----- Da: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di Antoine Terracol Inviato: venerdì 23 ottobre 2009 12.06 A: statalist@hsphsun2.harvard.edu Oggetto: Re: st: R: Problem with Left Truncation Hi, Carlo Lazzaro wrote:Dear Elaine, Please find beneath the following point-to-point comments about yourquery:<We are doing survival analysis, but unlike other dataset, our dataset only includes observations that have failed.> I would not be concerned about all failure=1; how long patient takes tofailure (failure time (tn)- risk onset (t0)) it's the relevant issue.I haven't done the math, but my intuition is the following. If Elaine's dataset can be considered as a random sample from the population, then she can use -stset- and proceed as usual. I can think of one case where it would not be true: Consider the case where individuals cannot be at risk before a certain calendar date t0 (say, because she is studying spells in a social program that did not exist before). If Elaine's observation window is relatively (compared to the average real duration in the state under study) short, and begins relatively (again, compared to the real durations) close to t0, then Elaine's sample will only contain spells short enough to have failed during the observation window. In this cas, the coefficients will be biased (although I'm not quite sure if there is a way to handle that with Stata). On the other hand, if the spells could have started at any given date before the observation window (or long enough before the start of the observation window, relatively to the real durations), then I think her sample will be random and can be analysed as usual. HTH, Antoine

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**References**:**R: st: R: Problem with Left Truncation***From:*"Carlo Lazzaro" <carlo.lazzaro@tin.it>

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