[SciPy-Dev] Resolving PR 235: t-statistic = 0/0 case

Ralf Gommers ralf.gommers@googlemail....
Sat Jun 9 06:04:29 CDT 2012


On Thu, Jun 7, 2012 at 10:13 PM, Nathaniel Smith <njs@pobox.com> wrote:

> On Thu, Jun 7, 2012 at 5:29 AM, Junkshops <junkshops@gmail.com> wrote:
> > - I'll merge the two 2 sample t-test functions
> > - add an uneq_var=False kw arg, setting to true will use the new code
>
> equal_var would be a better name, to avoid the double-negative.
>
> Would it be possible/desireable to make equal_var=False the default?
> Obviously this would require a deprecation period, but as semantic
> changes go it's relatively low risk -- anyone who misses the warnings
> etc. would just find one day that their t tests were producing more
> conservative/realistic values.
>

I'm not in favor of adding a deprecation warning for this. It's a minor
thing, and warnings are annoying - it does require the user to go and
figure out what changed. My preference would be to merge the current PR as
is, and add a new function that combines all four t-tests with an interface
similar to R. There the new default can be equal_var=False without annoying
anyone.


>
> (R defaults to doing the unequal variances test, and I have actually
> seen this fact used in their advocacy, as evidence for their branding
> as the tool for people who care about statistical rigor and
> soundness.)
>
> > - add an zoz=np.nan kw arg and a check that it's np.nan, 0 or 1.
> > Otherwise raise ValueError
>
> Let's please not add this "zoz=" feature. Adding features has a real
> cost (in terms of testing, writing docs, maintenance, and most
> importantly, the total time spent by all users reading about this
> pointless thing in the docs and being distracted by it). It's only
> benefit would be to smooth over this debate on the mailing list; I
> can't believe that any real user will actually care about this, ever.
>

Agreed.

And +1 for 0/0 --> NaN.

Ralf
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