On Thu, Mar 28, 2013 at 5:07 AM, rm <r...@wippies.se> wrote:
>
> While testing that I get the same results with the package survey as with
> the package survival, I encountered the issue of how to draw survival
> curves. Apparently the implementations in the two packages differ, as I
> show below.
>
> I would very much welcome your views, since the tail of the survival curve
> has a major impact on the interpretation of my results. In my data, the
> last
> ‘death’ occurs at 2094 days, while the last censoring time is 3297 days.
> If
> possible, I would like to say something about the probability between 2100
> days and 3300 days.
>
> So, my question is that after the last observed death, in the very simple
> example below at 883 days, how should one draw the survival curve? The
> graph
> produced by svykm (package survey) ends at 883 days, whereas survfit
> (package survival) continues the graph all the way to the last censoring
> time, which is at 1022 days.
>
If you don't ask for standard errors, svykm() also draws the curve all the
way out to 1022 days. The problem is with the standard error estimation
under complex sampling -- to save memory it computes the standard errors
only at event times. It shouldn't be too hard to get it to extend that to
the last censoring time, but the reason it isn't too hard is that the curve
and standard error estimates don't change after the last failure time, so
it won't be particularly useful.
-thomas
--
Thomas Lumley
Professor of Biostatistics
University of Auckland
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