[Numpy-discussion] varu and stdu

Kevin Jacobs <jacobs@bioinformed.com> bioinformed@gmail....
Mon Apr 7 10:43:30 CDT 2008


I know I'm off topic and maybe a day late, but I'm pained by the naming of
ddof.

It is simply not intuitive for anyone other than the person who thought it
up (and from my recollection, maybe not even for him).    For one, most
stats folk use 'df' as the abbreviation for 'degrees of freedom'.  Secondly,
the we tend to think of the constant bias adjustment as an ~adjustment~ of
the sample size or df.  So 'df_adjust=0' or 'sample_adjust=0' will resonate
much more.

The other issue is to clearly describe if 'N-1' is obtained by setting the
adjustment (whatever it is called) to +1 or -1.  There is a reason why most
stats packages have different functions or take a parameter to indicate
'sample' versus 'population' variance calculation.  Though don't take this
as a recommendation to use var and varu -- rather I'm merely pointing out
that var(X, vardef='sample') is an option (using SAS's PROC MEANS parameter
name as an arbitrary example).

In the extremely rare cases I need any other denominator, I'm fine with
multiplying by var(x)*n/(n-adjust).

-Kevin


On Mon, Apr 7, 2008 at 9:41 AM, Pierre GM <pgmdevlist@gmail.com> wrote:

> Anne, Travis,
> I have no problem to get rid of varu and stdu in MaskedArray: they were
> introduced for my own convenience, and they're indeed outdated with the
> introduction of the ddof parameters. I'll get rid of them next time I post
> something on the SVN.
>
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