[Numpy-discussion] Standard Deviation (std): Suggested change for "ddof" default value

Daπid davidmenhur at gmail.com
Fri Apr 4 08:50:08 EDT 2014


On 2 April 2014 16:06, Sturla Molden <sturla.molden at gmail.com> wrote:

> <josef.pktd at gmail.com> wrote:
>
> > pandas came later and thought ddof=1 is worth more than consistency.
>
> Pandas is a data analysis package. NumPy is a numerical array package.
>
> I think ddof=1 is justified for Pandas, for consistency with statistical
> software (SPSS et al.)
>
> For NumPy, there are many computational tasks where the Bessel correction
> is not wanted, so providing a uncorrected result is the correct thing to
> do. NumPy should be a low-level array library that does very little magic.


All this discussion reminds me of the book "Numerical Recipes":

"if the difference between N and N - 1 ever matters to you, then you
are probably up to no good anyway -- e.g., trying to substantiate a
questionable
hypothesis with marginal data."

For any reasonably sized data set, it is a correction in the second
significant figure.
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