[SciPy-Dev] ttest_1samp strange behaviour

[James Bergstra]

I appreciate that I presented a corner case, but your example gives
something even more bizarre: the two-tailed p-value jumps erratically almost
all the way between 0 and 1 on adjacent calls!  Shouldn't it hold steady and
approach 1?

On Fri, May 20, 2011 at 5:04 PM, <josef.pktd at gmail.com> wrote:

> On Fri, May 20, 2011 at 4:56 PM, James Bergstra
> <james.bergstra at gmail.com> wrote:
> > I was trying to make sure that ttest_1samp did what I thought and came
> > across the following...
> > In [41]: for i in range(10):
> >    ....:     print scipy.stats.ttest_1samp([0]*i, 0)
>
> I don't know if this makes sense, variance is zero in your case
>
> try something like
>
> for i in range(2,1000,10):
> print(stats.ttest_1samp(1e-10*np.random.randn(i), 0))
>
> Josef
>
> >    ....:
> >    ....:
> > (nan, nan)
> > (1.0, nan)
> > (1.0, 0.49999999999999956)
> > (1.0, 0.42264973081037427)
> > (1.0, 0.39100221895577053)
> > (1.0, 0.37390096630005898)
> > (1.0, 0.36321746764912255)
> > (1.0, 0.35591768374958205)
> > (1.0, 0.35061666282020748)
> > (1.0, 0.34659350708733416)
> > Am I interpreting this correctly that the null-hypothesis is decreasing
> in
> > probability as we actually observe it more times??
> >
> > James
> > --
> > http://www-etud.iro.umontreal.ca/~bergstrj
> >
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> >
> >
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-- 
http://www-etud.iro.umontreal.ca/~bergstrj
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