Paul Brandon wrote:
> At 10:10 AM -0500 9/23/00, Stuart Mckelvie wrote:
> >Dear Tipsters,
> >
> >One reason we use the standard deviation is that it comes from the
> >family of functions called moments about the origin of the
> >distribution:
> >
> >Moment (r) = E[(X - mean) to power r]
> >
> >(sorry that the program does not give proper symbols)
> >
> >So the first moment = E[X - mean] = E(x) - E(mean) = mean -mean = 0
> >
> >The second momen = E[(X - mean)squared] = variance
> >
> >The third mean reflect symmetry or skewness.
>
> This is probably the best answer yet.
> In physics, the first, second and third moments (I think; my reference is
> in my office and I'm not) correspond to frequency, rate and acceleration.
Yes - this is correct. Also, the statistical procedures which follow in most
stats classes (ANOVA, regression) are also based on squared deviations about
the mean. i.e. Sum of squares is just sum of _squared_ deviations around the
mean - not sum of absolute value of deviations scores.
--
---------------------------------------------------------------
John W. Kulig [EMAIL PROTECTED]
Department of Psychology http://oz.plymouth.edu/~kulig
Plymouth State College tel: (603) 535-2468
Plymouth NH USA 03264 fax: (603) 535-2412
---------------------------------------------------------------
"What a man often sees he does not wonder at, although he knows
not why it happens; if something occurs which he has not seen before,
he thinks it s marvel" - Cicero.
