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RE: st: Wald interval and the WSJ


From   "Lachenbruch, Peter" <Peter.Lachenbruch@oregonstate.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Wald interval and the WSJ
Date   Thu, 14 Aug 2008 09:28:31 -0700

Using the data from the paper (same as Maarten's) I got


. tabi 102 872\69 793,row

           |          col
       row |         1          2 |     Total
-----------+----------------------+----------
         1 |       102        872 |       974 
           |     10.47      89.53 |    100.00 
-----------+----------------------+----------
         2 |        69        793 |       862 
           |      8.00      92.00 |    100.00 
-----------+----------------------+----------
     Total |       171      1,665 |     1,836 
           |      9.31      90.69 |    100.00 

Upper bound of two-sided confidence interval

. disp (.1047-.08)+1.96*sqrt(.1047*(1-.1047)/974+.08*.92/862)
.05111444

Non-inferiority test

. disp (.1047-.08-.03)/sqrt(.1047*(1-.1047)/974+.08*.92/862)
-.39326968

I don't seem to be able to reproduce the z needed for a p of 0.0484...

Tony

Peter A. Lachenbruch
Department of Public Health
Oregon State University
Corvallis, OR 97330
Phone: 541-737-3832
FAX: 541-737-4001


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Maarten buis
Sent: Thursday, August 14, 2008 8:09 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Wald interval and the WSJ

--- David Airey <david.airey@Vanderbilt.Edu> wrote:
> And also the article doesn't emphasize effect size, which might make
> the quibbling over p values moot too.

Actually, the point estimate seems to suggest that the new stent does
better then the old one, if I read the original article
(http://content.onlinejacc.org/cgi/content/full/49/16/1676) correctly,
and I know absolutely nothing about cardiology other than that a
working hart is sorta crucial in staying alive.

I read this article as follows: The thing under study is how well two
types of stents prevent a thing called TVR (target vessel
revascularization) which is apperently a bad thing. In the group with
old stents this occured 68 times out of 855 (7.95%), while in the group
with new stents this occured 67 out of 956 times (7.01%). The purpose
of this study is to test the hypothesis that the proportion new -
porportion old > .03 . 

I have been looking around if I could reproduce the tests reported in
the Wall Street Journal using Stata, but remained unsuccesful. This
probably says more about me than about Stata, because statistically
this is also unfamiliar terain for me, as I almost always do some sort
of regression, moreover if I where to look at tests like these I would
probably prefer odds ratios rather than risk differences. 

-- Maarten

-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------

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