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From |
Steven Samuels <ssamuels@albany.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: repeat: predict after -streg- |

Date |
Thu, 12 Jul 2007 10:32:41 -0400 |

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 EFax: 208-498-7441 * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: repeat: predict after -streg-***From:*Jeph Herrin <junk@spandrel.net>

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