[issue20389] clarify meaning of xbar and mu in pvariance/variance of statistics module

[Irit Katriel]

Irit Katriel  added the comment:

I've closed issue36099 as a duplicate of this.

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[issue20389] clarify meaning of xbar and mu in pvariance/variance of statistics module

[Irit Katriel]

Change by Irit Katriel :


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keywords: +easy
versions: +Python 3.10, Python 3.11, Python 3.9 -Python 3.4

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[issue20389] clarify meaning of xbar and mu in pvariance/variance of statistics module

[Nick Coghlan]

Nick Coghlan added the comment:

Steven included some draft docs updates in a separate patch for issue 20481 - I 
have split those out and uploaded them here (since this discussion refers to 
the docstrings as well).

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nosy: +ncoghlan
Added file: http://bugs.python.org/file33990/issue20389_statistics_docs.diff

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[issue20389] clarify meaning of xbar and mu in pvariance/variance of statistics module

[Oscar Benjamin]

Oscar Benjamin added the comment:

I agree that the current wording in the doc-strings is ambiguous. It should be 
more careful to distinguish between

mu : true/population mean
xbar : estimated/sample mean

I disagree that the keyword arguments should be made the same. There is an 
important conceptual difference between these two things that the user needs to 
be aware of and mu, xbar - as symbols rather than ascii characters - are widely 
used for this. See e.g. this Wikipedia entry (although it uses ybar instead of 
xbar):
http://en.wikipedia.org/wiki/Variance#Population_variance

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[issue20389] clarify meaning of xbar and mu in pvariance/variance of statistics module

[Steven D'Aprano]

Changes by Steven D'Aprano steve+pyt...@pearwood.info:


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assignee:  - stevenjd
nosy: +stevenjd

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[issue20389] clarify meaning of xbar and mu in pvariance/variance of statistics module

[Julian Taylor]

Changes by Julian Taylor jtaylor.deb...@googlemail.com:


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[issue20389] clarify meaning of xbar and mu in pvariance/variance of statistics module

[Julian Taylor]

New submission from Julian Taylor:

the pvariance and variance functions take the argument mu and xbar to pass the 
population and sample mean to avoid some recomputation.

I assume the keyword arguments are different because the two means accepted are 
different, but the docstring does not indicate this directly.
It just says mu or xbar is the mean of the data. The module documentation is a 
little clearer but only in the grey box right at the end.

I would propose to change the docstring and module documentation to explicitly 
state that mu is the population mean and xbar is the population mean.
E.g.

- The optional argument mu, if given, should be the mean of
the data.
+ The optional argument mu, if given, should be the population mean of
the data.

etc.

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messages: 209192
nosy: jtaylor
priority: normal
severity: normal
status: open
title: clarify meaning of xbar and mu in pvariance/variance of statistics module
versions: Python 3.4

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[issue20389] clarify meaning of xbar and mu in pvariance/variance of statistics module

[Julian Taylor]

Julian Taylor added the comment:

xbar is the *sample* mean of course

maybe with proper docstrings the two functions could also use the same keyword 
argument?

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