Re: Variance as central moment

Hilarious, incredible, anecdotic!


Firstly the CONSULT:

Author: shehry@xxxxxxxxx
*** Hi,
i am new to statistics and i was reading the 'variance' and the'central moment' pages at wikipedia. I read that variance was the second central moment. And that the idea of the central moments came in from the moment theory in physics. i have been trying to relate the two concepts (moment in physics and moment in stats) but i am still not sure. the way i see it, variance gives the spread about the mean position (the axis of rotation). but is that the only relationship between the physics and stats concept??? plus i read that the third and the fourth central moments are skewness and kurtosis. can i get any help concerning regarding those two as well. i would really like to know how they came to be known as the third and fourth central moments.
thanks ***


To which Richard Ulrich answered:

***First and second *moments*, and so on, are named from the power of x, x^1, x^2, x^3, ... , which uses the raw values. You can look at the total or (more often) the average. The "central" moment is a re-definition that centers around the mean. It is also useful, for statisticians at least, to use versions of the 3rd-and-higher central moments that are "standardized" to be dimensionless. There are several formulas for skewness and kurtosis, which vary in how they are standardized. As I mentioned, "3rd" and "4th" are the powers. -- ***

My comment

The <expert consultant> could not understand what was asked! The dyslexic guy seems to ignore that the <MOMENT of INERTIA> in Mechanic that was adopted by the Statisticians because the formula to find this quantity is similar to the so-called 2nd MOMENT.
It deals with acelerating masses that could rotate around an axis or a point.
The full explanation can be found at (GOOGLE)
em-ntserver.unl.edu/Negahban/em373/note18/note18.htm - 36k -
________licas (Luis A. Afonso)
.

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