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Re: st: Different results using stdes and stsum


From   moleps islon <moleps2@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Different results using stdes and stsum
Date   Wed, 7 Oct 2009 14:23:27 +0200

And using SPSS (for a change in environment) I get median overall
survival 9.9 months.

So I have stsum giving 10.1 months median survival time, I have stdes
giving 9.6 months time at risk and SPSS giving me 9.9 months.

I assume the difference between stdes and stsum is related to how you
treat the still patients not dead yet since the values are identical
for -stsum/stdes if status_fu==0-, equal to 8.6 months. The 8.6 months
would then be the patients already dead and I guess the increased time
you see above is related to the fact that the still living patients
contribute to increasing this value. However why should there be a
difference between the time-at risk and the survival time for the
living? And why is there a difference for all these values when I
compare to SPSS.

regards,

m





On Wed, Oct 7, 2009 at 1:16 PM, moleps islon <moleps2@gmail.com> wrote:
> Dear listers,
> using stata v10.1 I obtain different results in my dataset for the
> median survival using stsum and stdes for the dataset, i.e.
>
> . stdes
>
>         failure _d:  status_fu == 0
>   analysis time _t:  cox_time
>
>                                   |-------------- per subject --------------|
> Category                   total        mean         min     median        max
> ------------------------------------------------------------------------------
> no. of subjects              516
> no. of records               516           1           1          1          1
>
> (first) entry time                         0           0          0          0
> (final) exit time                   11.66499    .0666667   9.633333       74.9
>
> subjects with gap              0
> time on gap if gap             0
> time at risk           6019.1333    11.66499    .0666667   9.633333       74.9
>
> failures                     453     .877907           0          1          1
> ------------------------------------------------------------------------------
>
> . help sts
>
> . stsum
>
>         failure _d:  status_fu == 0
>   analysis time _t:  cox_time
>
>         |               incidence       no. of    |------ Survival time -----|
>         | time at risk     rate        subjects        25%       50%       75%
> ---------+---------------------------------------------------------------------
>   total |  6019.133335     .07526           516   4.733333  10.06667  17.03333
>
>
> What is the difference in median time at risk per subject and median
> survival time? Which one to report?
>
> regards,
>
> M
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