Re: Skewness


""Luis A. Afonso"" <licas_@xxxxxxxxxxx> wrote in message
news:2756312.1114345179036.JavaMail.jakarta@xxxxxxxxxxxxxxxxxxxxxxxxx
> Skewness of normal standard samples
>
>
> Here are the size-dependent confidence intervals I found: .(the program
> listing relative to these results was posted in the thread Kurtosis,
> skewness and bootstrapping, Tim De Meyer, my Re:)
>
> size=10 p[-1.162 , 1.162]=95%
> p[-1.580 , 1.580]=99%
>
> size=20 p[-0.942 , 0.942]=95%
> p[-1.312 , 1.312]=99%
>
> size=25 p[-0.866 , 0.866]=95%
> p[-1.207 , 1.207]=99%
>
> size=30 p[-0.805 , 0.805]=95%
> p[-1.814 , 1.814]=99%
>
> There is a post from James Dean Brown (University of Haway at Manoa
> www.jalt.org/test/bro_1.htm) where the following formula provides the
> confidence interval (95%) ( Barbara Tabachnick & Linda Fidell):
>
> [-1.960*Sqrt(k/size), 1.960*sqrt(k/size)]
> being k=6.
>
> This formula is approximate (as it is well known): this Table shows how
> accurate for small sizes:
>
> Size=10, k=3.515
> Size=20, k=4.620
> Size=25, k=4.880
> Size=30, k=5.061
>
> The T&F formula should be used for medium-large sizes, I presume.
>
> Licas_@xxxxxxxxxxx
+++++++++++++++++++++++++++++++++++++
The formula is way off. Somebody never did a literature search here. Look up
the works by D'Agostino.

David Heiser



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