On 11/29/2016 05:00 AM, r-help-request at r-project.org
wrote:> Independent censoring is one of the fundamental assumptions in the survival
analysis. However, I cannot find any test for it or any paper which discusses
how real that assumption is.
>
>
> I would be grateful if anybody could point me to some useful references. I
have found the following paper as an interesting reference but it is not freely
available.
>
>
> Leung, Kwan-Moon, Robert M. Elashoff, and Abdelmonem A. Afifi.
"Censoring issues in survival analysis." Annual review of public
health 18.1 (1997): 83-104.
>
>
This is because there is no test for independent censoring. Say I am following
a cohort
of older gentlemen (65 years old) who were diagnoses with condition
"x", and after 8 years
there a a dozen who no longer answer my letters. Why not?
a. Perhaps because they are in a nursing home, with dementia.
b. Perhaps because they have moved to another city to be interact and be near
to
grandchildren.
In case a, those lost to follow-up are much sicker than the average subject, and
in case b
they are most likely the most healthy and active of the group. In a) the KM
will
over-estimate survival and in b it will underestimate.
The main point is that there is absolutely no way to know, other than actually
tracking
the subjects down. Any study which has a substantial fraction with incomplete
follow-up
is making a guess. The more accurate phrase would be "a blind hope for
independent
censoring" than "assume". There are cases where simple
reasoning or experience tells me
that this hope is futile, but mostly we just hope. The alternative is proactive
follow-up, i.e., devote enough staff and resources to actively contact all of
the study
subjects on a regular schedule. Even then you will lose a few. (In one study
several
years ago, long term follow-up of cancer, there was a new Mrs Smith who refused
to
acknowledge the existence of the prior wife, even to forward letters.)
Terry Therneau