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RE: st: Confidence limits on survival probabilities from stcox


From   "CDSC - Verlander, Neville" <Neville.Verlander@hpa.org.uk>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Confidence limits on survival probabilities from stcox
Date   Tue, 1 Feb 2005 10:01:26 -0000

Dear stata users

Thanks for Ricardo's idea, but there are two problems: one that the
estimates obtained are not the same as those that stcurve plots (perhaps the
fact that my covariates are categorical variables with more than 2 levels I
may have used the adjustfor option in the wrong way - I put in the dummy
variables, except the baseline ones - so I stand to be corrected on this
one) and two, that one only gets a listing at the time points in the dataset
and not at all the time points.

Here is a snippet of code which gives one of the graphs with 8 curves
corresponding to the 8 sizegroups (similarly for the other 12 countries).
Regarding point one, I can't reproduce the values in the output file
cox1.dta using the sts list command - I've tried using both the by and
adjustfor commands. Assuming one can reproduce the values, how does one
overcome point two above? 

xi i.sizegrp i.cogrp;
ren _Isizegrp_2 s2;
ren _Isizegrp_3 s3;
ren _Isizegrp_4 s4;
ren _Isizegrp_5 s5;
ren _Isizegrp_6 s6;
ren _Isizegrp_7 s7;
ren _Isizegrp_8 s8;
ren _Icogrp_2 c2;
ren _Icogrp_3 c3;
ren _Icogrp_4 c4;
ren _Icogrp_5 c5;
ren _Icogrp_6 c6;
ren _Icogrp_7 c7;
ren _Icogrp_8 c8;
ren _Icogrp_9 c9;
ren _Icogrp_10 c10;
ren _Icogrp_11 c11;
ren _Icogrp_12 c12;
ren _Icogrp_13 c13;
stcox s2 s3 s4 s5 s6 s7 s8 c2 c3 c4 c5 c6 c7 c8 c9 c10 c11 c12 c13, robust
basesurv(surv);
stcurve,
at1(s2=0,s3=0,s4=0,s5=0,s6=0,s7=0,s8=0,c2=0,c3=0,c4=0,c5=0,c6=0,c7=0,c8=0,c9
=0,c10=0,c11=0,c12=0,c13=0) 
 
at2(s2=1,s3=0,s4=0,s5=0,s6=0,s7=0,s8=0,c2=0,c3=0,c4=0,c5=0,c6=0,c7=0,c8=0,c9
=0,c10=0,c11=0,c12=0,c13=0) 
 
at3(s3=1,s2=0,s4=0,s5=0,s6=0,s7=0,s8=0,c2=0,c3=0,c4=0,c5=0,c6=0,c7=0,c8=0,c9
=0,c10=0,c11=0,c12=0,c13=0) 
 
at4(s4=1,s3=0,s2=0,s5=0,s6=0,s7=0,s8=0,c2=0,c3=0,c4=0,c5=0,c6=0,c7=0,c8=0,c9
=0,c10=0,c11=0,c12=0,c13=0) 
 
at5(s5=1,s3=0,s4=0,s2=0,s6=0,s7=0,s8=0,c2=0,c3=0,c4=0,c5=0,c6=0,c7=0,c8=0,c9
=0,c10=0,c11=0,c12=0,c13=0)
 
at6(s6=1,s3=0,s4=0,s5=0,s2=0,s7=0,s8=0,c2=0,c3=0,c4=0,c5=0,c6=0,c7=0,c8=0,c9
=0,c10=0,c11=0,c12=0,c13=0) 
 
at7(s7=1,s3=0,s4=0,s5=0,s6=0,s2=0,s8=0,c2=0,c3=0,c4=0,c5=0,c6=0,c7=0,c8=0,c9
=0,c10=0,c11=0,c12=0,c13=0) 
 
at8(s8=1,s3=0,s4=0,s5=0,s6=0,s7=0,s2=0,c2=0,c3=0,c4=0,c5=0,c6=0,c7=0,c8=0,c9
=0,c10=0,c11=0,c12=0,c13=0)
         survival outfile(c:\work\data\cox1.dta,replace)
title("Country 1",size(medium) color(black)) xtitle("No. of weeks")
legend(label(1 "Sizegroup 1") label(2 "Sizegroup 2")
label(3 "Sizegroup 3") label(4 "Sizegroup 4") label(5 "Sizegroup 5") 
label(6 "Sizegroup 6") label(7 "Sizegroup 7") label(8 "Sizegroup 8"));

Once again, thank you for your attention and any assistance you can provide.

Regards,

Neville

----------------------------------------------------------------------------
----------------------------------------------

Neville Verlander
Statistics Unit
Statistics, Modelling and Economics Department
Health Protection Agency Centre for Infections
61 Colindale Avenue
London
NW9 5EQ

Tel: (direct) (+44) 0208 3277426
Fax: (+44) 0208 7868


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Ricardo Ovaldia
Sent: 31 January 2005 17:00
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Confidence limits on survival probabilities from stcox

--- "CDSC - Verlander, Neville"
<Neville.Verlander@hpa.org.uk> wrote:

> How can one obtain the 95% confidence limits on the survival 
> probabilities from multiple failure data following model estimation 
> using stcox and how is it different if one wants, say, a 70% 
> Confidence Interval? I know one can use sts list, but this only gives 
> Kaplan-Meier estimates giving quite different estimates to those from 
> stcox.

I think that you can use the -sts list- with the -adjustfor()-. Acording to
the help file it fits a Cox model.

Regards,
Ricardo.

=====
Ricardo Ovaldia, MS
Statistician
Oklahoma City, OK

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