[SciPy-user] information on statistical functions

Robert Kern robert.kern@gmail....
Wed Dec 17 20:03:27 CST 2008


On Wed, Dec 17, 2008 at 19:53,  <josef.pktd@gmail.com> wrote:
> On Wed, Dec 17, 2008 at 7:58 PM, Tim Michelsen
> <timmichelsen@gmx-topmail.de> wrote:
>> Hello,
>> I observed that there are 2 standard deviation functions in the
>> scipy/numpy modules:
>>
>> Numpy:
>> http://docs.scipy.org/doc/numpy/reference/generated/numpy.std.html#numpy.std
>>
>> Scipy:
>> http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.std.html#scipy.stats.std
>>
>> What is the difference?
>> There is no formula included within the docstrings.
>>
>> I suppose that np.std() is for the whole population and scipy.std is
>> designed for a smaller sample in the population.
>> Is that true?
>
> difference between population (numpy) and sample (scipy.stats)
> variance and standard deviation is whether the the estimator is
> biased, i.e. 1/n, or not, i.e. 1/(n-1).

It's a shame that the "biased/unbiased" terminology still survives in
the numpy.std() docstring. It's really quite wrong.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco


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