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Re: st: Wald interval and the WSJ


From   David Airey <david.airey@Vanderbilt.Edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Wald interval and the WSJ
Date   Thu, 14 Aug 2008 09:12:12 -0500

.

Another point of view is that for something like a stent that goes in a human body, I'd want my probability to be quite a bit better than . 05 anyway, like .01 or .001. I've seen a lot of .05 results evaporate on additional scrutiny. And also the article doesn't emphasize effect size, which might make the quibbling over p values moot too.

-Dave

On Aug 14, 2008, at 8:56 AM, Maarten buis wrote:


It looks to me (though the article doesn't say) that this deals with a
test of multinomial proportions. This is a difficult problem, the exact
test statistic exists, but is actually not exact at all but
conservative, various other/better approximations have been proposed,
but now you have to decide how to choose between them. In this case all
the different p-values are very close to .05 (from .049 to .052 whith a
spike at .55) The articles puts great emphasis on the fact that all but
one test results in p-values more then .05, and that the company
conveniently choose the one test that supported their claim. That may
or may not be suspicious, but my reading of a study like this is that
these numbers are so close to .05 (and there is nothing magical or
`scientific' about the number .05) that making a big deal about a black
and white distinction between significant and non-significant is pretty
ridiculous. I know that this doesn't help an agency like the FDA who
have to make a approve or disaprove decision (and they certainly don't
ask my advise), but sometimes a study just ends up in a grey area
between significant and insignificant.

-- Maarten

--- Scott Merryman <scott.merryman@gmail.com> wrote:


There is an interesting article in today's Wall Street Journal on the
use of the Wald interval in clinical trials.

"Boston Scientific Stent Study Flawed"  by Keith Winstein, August 14,
2008; Page B1.

"But Boston Scientific's claim was based on a flawed statistical
equation that favored the Liberte stent, a Journal analysis has
found.
Using a number of other methods of calculation -- including 14
available in off-the-shelf software programs -- the Liberte study
would have been a failure by the common standards of statistical
significance in research.
Boston Scientific isn't the only company to use the equation, known
as
a Wald interval, which has long been criticized by statisticians for
exaggerating the certainty of research results. "


http://digg.com/business_finance/WSJ_com_Boston_Scientific_Stent_Study_Flawed
Scott
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-----------------------------------------
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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