Comments on: Announce: New fraud detection website

By: Geoff Sherrington

Geoff Sherrington — Fri, 16 Jan 2009 12:04:46 +0000

In my laboratory times in the 70s, instruments often had meter readouts that the operator had to approximate while they moved gently to and fro. Unknown to the operators, we developed signatures for each of them based on the last digit. It was not infallible, but when you asked “Why did you do XYZ’s readings yesterday?” the body language and sometimes the admission often suggested you were right. So I explained to the staff what we were doing and the practice soon died out. It was sometimes complicated by log scales on the meters.

By: admin

admin — Fri, 16 Jan 2009 10:39:59 +0000

Rich: “why mention Benford’s Law at all?” Well on the plus side it puts it into context so people can research it. First digit has been used a lot, see Nigrini, second digit I have used in my book on measurement data. This is the first time I have seen last digits used. It’s not a law really.

By: Rich

Rich — Fri, 16 Jan 2009 09:43:51 +0000

#16 davids

That was rather my point. If what you’re doing is testing against a uniform distribution (and the table of results shows that you are) why mention Benford’s Law at all? True, the distribution of the Nth digit tends to uniform as N increases but so what?

No, it doesn’t matter but it confused me at the outset.

By: admin

admin — Fri, 16 Jan 2009 06:16:43 +0000

Steven: “Evidence of divergence is not proof of fraud or cheating.” That is right and I have said that. No insinuation in the title, detecting cheating is what the web site and these methods are mainly for.

Here is an analogy. You go to your doctor and he suggests a blood test for a condition, prostate cancer say. He tells you the test is not definitive, but if it comes back negative you are clear. The test comes back positive, and he suggests more extensive testing.

That is what is happening here. Do you accuse the doctor of insinuating you have prostate cancer? If it turns out you don’t have prostate cancer do you tell he’s wearing a tin hat for reporting that the first test came back positive?

Thanks for your comment anyway.

By: Steven Talbot

Steven Talbot — Fri, 16 Jan 2009 02:27:35 +0000

David Stockwell,

You state yourself that “there are a number of innocent reasons that digit frequency may diverge from expected”. Why, then, do you consider it proper to refer to “fraud detection” in your title and “cheating” in your subtitle? It seems to me that you are improperly insinuating such motives on the part of GISS, without respecting the responsibility of actually presenting any proof to support your implications. Evidence of divergence is not proof of fraud or cheating.

By: davids

davids — Thu, 15 Jan 2009 17:42:34 +0000

#Rich, Benfords Law tends to uniform in the subsequent digits. Anyway it doesn’t apply to measurement data, that can have a constant initial digit.

#John, http://landshape.org/check/check.txt

By: John

John — Thu, 15 Jan 2009 16:14:46 +0000

Can you make your script available? I don’t understand how the Pr values were derived.

By: Rich

Rich — Thu, 15 Jan 2009 13:15:38 +0000

Ang on a sec. Benford’s law is about the distribution of initial digits which follow a power law distribution. The test above is chi-squared against an assumed uniform distribution. Not the same animal at all.

By: Jan Pompe

Jan Pompe — Thu, 15 Jan 2009 06:40:58 +0000

“You should do this on all the lotto draws from last year. You may find THEY have been massaged too.”

I’m sure they have been :- I never win!!!

All very interesting.

By: David Stockwell

David Stockwell — Thu, 15 Jan 2009 06:18:18 +0000

Bishop, I would work backwards from the final data towards the station data, analysing intermediate data sets and trying to show how they change from stage to stage.