Re: Which prices are fake?

From: Bob Wheeler (bwheeler_at_echip.com)
Date: 09/18/04 

Date: Sat, 18 Sep 2004 14:46:40 -0400

Of course Benford's law doesn't help here, but as a hint, it suggests
that one should look at the digits, and the trailing digits suggest that
the first series is made up -- too many 0's for randomness. I don't
think I would say the same, had to told us that the first list was the
result of human scale reading, since the trailing digits for such tend
to mass on 0, 5, and 7.

Martin Penderis wrote:
> Richard Ulrich <Rich.Ulrich@comcast.net> wrote in message news:<uaemk01ubvbud11q669nogusfrrg284uro@4ax.com>...
>
>>On 17 Sep 2004 10:57:02 -0700, tafeltennis@mwpenderis.mailshell.com
>>(Martin Penderis) wrote:
>>
>>
>>>glenbarnett@geocities.com (Glen) wrote in message news:<bd343329.0409162012.4ca45af4@posting.google.com>...
>>>
>>>>tafeltennis@mwpenderis.mailshell.com (Martin Penderis) wrote in message news:<e4fa4b6f.0409161037.2f96728a@posting.google.com>...
>>>>
>>>>>One of the following two lists gives the closing prices of shares in a
>>>>>certain section (company names are not given). The other list was
>>>>>made up.
>>>>>List 1:
>>>>>84, 1347, 20, 202, 100, 829, 828, 970, 257, 540, 319, 605, 1591, 640,
>>>>>9900, 254, 310, 541, 487, 810, 415, 370, 96, 466, 274, 751, 540, 1660,
>>>>>1060, 490
>>>>>List 2:
>>>>>54, 462, 97, 2164, 850, 527, 53, 18, 46, 422, 69, 23, 555, 347, 933,
>>>>>4216, 666, 925, 89, 96, 197, 208, 58, 223, 652, 290, 765, 98, 222, 17
>>>>>Which list is the one that was made up? What is your reason for
>>>>>choosing that one?
>>>>>If you do not know where to start, do a search on Benford's rule.
>>>>
>>>>I suggest you do exactly as the last sentence says, and search
>>>>for "Benford's rule". It would have taken no more effort than
>>>>posting your homework did.
>>>>
>>>>Glen
>>>
>>>Homework?
>>>
>>>As a mathematician/statistician/somebody who is interested in
>>>statistics you should either not make assumptions, or have a valid
>>>reason for believing your assumption to be true.
>>
>>Well, gee, Martin, if you don't want your post to be
>>Replied to as if it were a homework problem -
>>posted in the laziest HW style (verbatim, including
>>the Teacher's hint) - then don't word it like
>>a homework problem.
>
>
> Do you have any suggestions for rewording? The post was meant as a
> challenge to all, and if the wording sounds like homework, I would not
> know. It has been many years. So far nobody has ventured to state one
> or the other, whether by guessing or otherwise. I added the hint
> because I believe this is neither something that is taught widely nor
> something often encountered in textbooks.
>
>>You've posted here occasionally (I see from group.google),
>>so you should have noticed that sci.stat.math suffers
>>from an excess of Homework posts. That's partly due to
>>link provided by Math Forum.
>>
>>You may have also noticed that if there is any
>>interesting complexity to the Original Post, it gets some
>>commentary anyway.
>>
>>
>>>One list was taken from a newspaper of 16 September (closing prices of
>>>the previous day). The other list was fabricated by me. This of course
>>>means that I do know the answer without having to do any calculations
>>>(actually I have forgotten which one, but that is no problem).
>>>
>>>If you go to sci.math you will see that I very recently posted a reply
>>>to someone who asked whether logarithms still had some use. In that I
>>>mentioned Benford's rule. That set me off to post something in this
>>>forum. I thought I would post it in this form; a few readers might
>>>find it interesting. I have done quite a lot of reading on Benford's
>>>rule.
>>
>>You might google also for "Zipf's Law" - it has more hits on
>>the Web, though fewer hits in Groups.
>
> "Mark Nigrini" is another good search, not necessarily in Google.
>
>>>The only purpose your post seems to have served is to put a block on
>>>the thread.
>>
>>Newbies should be warned off from answering homework -
>>that will only encourage - so that's fine with most of us.
>
> Yes, from answering homework. But does that mean something merely
> posted for the sake of interest should be thrown out as well? There
> seems to be a scarcity of that around here (I have seen a few posts
> with a religious slant, and other off-topic posts). 

-- 
Bob Wheeler --- http://www.bobwheeler.com/
         ECHIP, Inc. ---
Randomness comes in bunches.

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