Stephen Evans has done a great deal. You might also contact Jonas
Ranstam, Marc Buyse, or others. They did a survey a few years ago for
the ISCB on fraud.
There are many forms of fraud - data that are outliers (or inliers - too
good to be true), have decided digit preferences (too many 0s or 5s or
even numbers, etc.). I don't remember all.
However, there is a nice little book that was published about 10 years
ago that Evans had a chapter in and he used Mahalanobis's distance.
In another context, there was an issue at the FDA in which some lab
technicians were suspected of using the same data tray in blood testing
to avoid having to rerun the test if it didn't work out properly. This
would lead to almost identical values in the control wells, so we looked
at Euclidean distance between the plates that were close in time. We
also considered a rank procedure. I tried to explain the procedure to
the lawyers who were involved - they decided it was too complicated to
explain to a jury.
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: [email protected]
[mailto:[email protected]] On Behalf Of Maarten buis
Sent: Friday, September 26, 2008 9:58 AM
To: [email protected]
Subject: Re: st: Fraud methods in Stata
One way is to use Benford's Law, type -findit Benford's Law- and use
google to learn more.
Maarten
--- "Williams, Rachael" <[email protected]> wrote:
> Dear all,
>
> I am considering methods of detecting fraud in a hypothetical
> clinical
> trial with a large number of centres, but only a few patients per
> centre.
> In addition, many variables will be binary.
>
> Would Cook's D be appropriate here?
> Is it possible to calculate Mahalanobis' distance in Stata in order
> to
> detect (possibly fraudulent) inliers, outliers and near duplicates in
> a
> dataset?
>
> If anyone has any ideas of other ways to detect possible fraud I
> would
> love to hear from you too!
> Thanks - Rachael
>
>
>
>
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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 N515
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
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