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Re: st: intcens: how to estimate mean and variance after intcens


From   Yoann Madec <yoann.madec@pasteur.fr>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: intcens: how to estimate mean and variance after intcens
Date   Thu, 25 Oct 2012 10:43:54 +0200

Thanks steve for your comments, and sorry not to have mention the source of the intcens command.

After reading the help page for stpm, I still do not manage to make it work with interval-censored data.

As a test, I have written:

	gen date_left_censoring=seroco_d
	
	stset date_deb_periode1, scale(365.25) origin(seroco_d)

	failure(hiv_controleur_bis)

In this case, I should have no interval-censored data, but strictly right-censored data.
However, here is what STATA states:

. xi: stpm i.gender if num_v==1, stpmdf(6) scale(hazard) left(date_left_censoring)
i.gender          _Igender_1-2        (naturally coded; _Igender_1 omitted)
date_left_censoring>_t in some observations


I have been trying many things without success.

I hope someone can help.

Best regards,
Yoann

Le 12/10/2012 19:48, Steve Samuels a écrit :

Yoann, The FAQ ask that you state the source of unofficial commands.
-intcens- was written by Jamie Griffin and is available from SSC.

The usual sample descriptive statistics cannot be calculated for
interval-censored data.

One approach is to apply Patrick Royston's command -stpm-, also at SSC,
which fits flexible distributions. You can estimate survival curves and
percentiles of the unconditional as well as covariate-conditional,
distributions. You won't get standard errors for the percentiles, but
you could -bootstrap- these. Means and SDs can be estimated with a lot
more work, but I don't think these are useful descriptive stats for
most survival data problems.

In fact, I recommend -stpm-, not -intcens- for your main analysis. Some
reasons: 1) Both fit parametric models, but -stpm- adapts to the shape
of the distribution, saving you the need to select a "best" theoretical
distribution. 2) -stpm- has excellent postestimtion options; -intcens-
has none. (You can estimate survival curves&  statistics starting with
the supplied e(b) matrix, but you must do it by hand.) 3) -stpm- allows
coefficients to vary with time (i.e. time-predictor interactions,);
-intcens- does not.


Steve



On Oct 11, 2012, at 12:35 PM, Yoann Madec wrote:

Dear Stata users,

In order to describe the time to an event I used the command intcens. Indeed, for all my subjects, I know that the event took place within a time-interval, but do not have thje exact date.

Using intcens, I vcan test whether some factors influence this time to event.

However, I would like to summarize the time to event and provide a confidence interval for this time.
I have not been able to fin how to estimate a mean and variance after intcens.

i hope that someone will be able to help.

Best regards,

Yoann

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