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#1
05-20-2004, 11:27 PM
 KarlGauss Out of the slimy mud of words Charter Member Join Date: Mar 2000 Location: Between pole and tropic Posts: 6,376
Most commonly appearing first digit in (large) lists of numbers

A while ago in a GQ thread, someone mentioned what I believe were two related theorems in statistics.

The first theorem was something along the lines of "if you have a list of items (such as city populations) ranked by order of magnitude, the kth item will be approximately 1/kth of the largest", eg. the third city on a list of citys' populations will be approximately 1/3 that of the largest city.

The second theorem said that something along the lines of "in lists of numbers (such as street addresses or country's GNP's), more numbers will start with '1' than '2', and more '2s' than '3s' etc."

I know this is pretty vague but hope you can point me to the link/thread.

Thanks
#2
05-20-2004, 11:46 PM
 Squink Guest Join Date: Oct 2000
Quote:
 Known as Benford's law, it is a rule obeyed by a stunning variety of phenomena, from stock market prices to census data to the heat capacities of chemicals. Even a ragbag of figures extracted from newspapers will obey the law's demands that around 30 per cent of the numbers will start with a 1, 18 per cent with a 2, right down to just 4.6 per cent starting with a 9.
From The Power of One

Benford's Law at Mathworld

New Scientist ran an article on the subject in July 1999.
#3
05-20-2004, 11:55 PM
 Wendell Wagner Charter Member Join Date: Jul 1999 Location: Greenbelt, Maryland Posts: 11,189
The first one is Zipf's Law:

http://www.cut-the-knot.org/do_you_know/zipfLaw.shtml
#4
05-20-2004, 11:56 PM
 KarlGauss Out of the slimy mud of words Charter Member Join Date: Mar 2000 Location: Between pole and tropic Posts: 6,376
Indeed!

Thank you both.
#5
05-21-2004, 06:02 PM
 Chronos Charter Member Join Date: Jan 2000 Location: The Land of Cleves Posts: 50,709
By the way, neither of those is a theorem. The first might be an empirical rule of thumb, good for many situations, but it's far from universal. The second-tallest man in the world, for instance, is not half the height of the tallest man in the world. Really, it's just a statement that a certain sort of distribution is common in the real world.

The second might be the bare-bones nugget of a provable statement, but you would need a lot more specification about the distributions, etc., to make it proveable.
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#6
05-21-2004, 07:35 PM
 KarlGauss Out of the slimy mud of words Charter Member Join Date: Mar 2000 Location: Between pole and tropic Posts: 6,376
You are quite right, Chronos. I was being lazy by using the term "theorem".

But teach me, though, please. Isn't "Benford's law", as described in the Mathworld link above (which I don't really understand) pretty close to a theorem?

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