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Re: st: Wald interval and the WSJ

From   Maarten buis <>
Subject   Re: st: Wald interval and the WSJ
Date   Thu, 14 Aug 2008 14:56:46 +0100 (BST)

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 <> 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. "
> 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

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