Re: st: repeat: predict after -streg-

[Steven Samuels <ssamuels@albany.edu>]

Jeph, -streg- is fitting censored parametric distributions (one for  
each combination of predictors) .  Most of the "true" unobserved  
failure times are >30 days, so the medians of the fitted  
distributions will be >30 days.  In rough terms, you are estimating  
entire distributions without data beyond the 22nd percentile.

-Steve

On Jul 12, 2007, at 9:10 AM, Jeph Herrin wrote


> I posted this a few days ago, but got no replies;
> thought I'd try again, shorter
>
>
> My data are time to readmission (failure) after
> hospitalization, with censoring on death:
>
> -> stset ftime, failure(radm)
>
>      failure event:  radm != 0 & radm < .
> obs. time interval:  (0, ftime]
>  exit on or before:  failure
>
> ---------------------------------------------------------------------- 
> --------
>    424787  total obs.
>         0  exclusions
> ---------------------------------------------------------------------- 
> --------
>    424787  obs. remaining, representing
>     95529  failures in single record/single failure data
>  1.07e+07  total analysis time at risk, at risk from t =         0
>                              earliest observed entry t =         0
>                                   last observed exit t =        30
>
> My model is
>
> . streg `mycovars' , d(lnormal)
>
> And my problem is:
>
>  . predict median, median time
>  . count if median<=30
>     30
>
> So, though the data have 95,000+ failures in less than 30 days, my
> model predicts only 30 such failures.
>
> I get the same results with other parameterizations, though lognormal
> seems the best fit. Either I don't understand what the model is doing,
> or I'm not calculating the correct predicted value. Should I expect
> this?
>
> Thanks in advance for any insights.
>
>
> Jeph
>
>
> *
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Steven JH Samuels
845-246-0774
18 Cantine's Island
Saugerties, NY 12477
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*
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