[Python-ideas] Pre-PEP 2nd draft: adding a statistics module to Python

[Oscar Benjamin]

On 9 August 2013 07:43, Steven D'Aprano <steve at pearwood.info> wrote:
> On 09/08/13 12:39, Stephen J. Turnbull wrote:
>>
>> Steven D'Aprano writes:
>>
>>   > [2] But which ones? I know of at least four different definitions
>>   > of each [of skew and kurtosis], three of which are in common
>>   > use. Annoyingly, the differences are not documented.
>>
>> Do you mean "definitions" or "implementations"?
>
>
> Yes :-)
>
> Or possibly both. Skew and kurtosis are especially egregious examples of
> mathematicians being inconsistent in their terminology, notation and
> definitions, but as far as I have been able to determine, there are three
> common formulae for the third moment about the mean skewness:

Perhaps they just shouldn't be included then. Does anyone here
*really* have an application for computing skewness/kurtosis (don't
just imagine one)?

I don't think I ever compute these directly although I have used
normality tests that might have used them internally (i.e. for the
D'Agostino K-squared test as computed by numpy's skewtest function). I
would find skew and kurtosis functions not very useful unless I also
have the appropriate statistical tests and statistical testing is a
massive can of worms.


Oscar