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

[Steve Samuels <sjsamuels@gmail.com>]

Without seeing your data, we cannot possibly diagnose your problem. I
consider it a mistake to use scale(365.25): 365.25 is not a natural unit
since no number of days will equal it. In any case, we need to see the
original date values, so omit the scale() option from -stset-.

Have you examined the sources of the message from Stata? [NB: not
"STATA"]

************************************************* list _t
date_left_censoring date_deb_periode1 if date_left_censoring>_t
***************************************************

Do this after formatting all the listed values, including _t with %td.
It's not necessary to run -stpm- to get this listing, as all values are
available after -stset-.


Steve

On Oct 25, 2012, at 4:43 AM, Yoann Madec wrote:

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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