[R] "chi-square" | "chi-squared" | "chi squared" | "chi square" ?

[Richard M. Heiberger]

What a delightful question.  Bill Cochran discussed this in class
one day about 50 years ago.  He said the British usage (which I think
he said was chi-squared,
as is consistent with the other memories in this thread)
is what he learned and previously used.  But he had been in the US for
so long that he was now using
the American preference (chi-square).

Rich

On Fri, Oct 18, 2019 at 8:51 AM Martin Maechler
<maechler using stat.math.ethz.ch> wrote:
>
> As it's Friday ..
>
> and I also really want to clean up help files and similar R documents,
> both in R's own sources and in my new 'DPQ' CRAN package :
>
> As a trained mathematician, I'm uneasy if a thing has
> several easily confusable names, .. but as somewhat
> humanistically educated person, I know that natural languages,
> English in this case, are much more flexible than computer
> languages or math...
>
> Anyway, back to the question(s) .. which I had asked myself a
> couple of months ago, and already remained slightly undecided:
>
> The 0-th (meta-)question of course is
>
>   0. Is it worth using only one written form for the
>      χ² - distribution, e.g. "everywhere" in R?
>
> The answer is not obvious, as already the first few words of the
> (English) Wikipedia clearly convey:
>
> The URL is  https://en.wikipedia.org/wiki/Chi-squared_distribution
> and the main title therefore also
>     "Chi-squared distribution"
>
> Then it reads
>
> > This article is about the mathematics of the chi-squared
> > distribution. For its uses in statistics, see chi-squared
> > test. For the music [...]
>
> > In probability theory and statistics, the chi-square
> > distribution (also chi-squared or χ2-distribution) with k
> > degrees of freedom is the distribution of a sum of the squares
> > of k independent standard normal random variables.
>
> > The chi-square distribution is a special case of the gamma
> > distribution and is one of the most widely used probability
> > distributions in inferential statistics, notably in hypothesis
> > testing [........]
> > [........]
>
> So, in title and 1st paragraph its "chi-squared", but then
> everywhere(?) the text used "chi-square".
>
> Undoubtedly, Wilson & Hilferty (1931) has been an important
> paper and they use "Chi-square" in the title;
> also  Johnson, Kotz & Balakrishnan (1995)
> see R's help page ?pchisq use  "Chi-square" in the title of
> chapter 18 and then, diplomatically for chapter 29,
>  "Noncentral χ²-Distributions" as title.
>
> So it seems, that historically and using prestigious sources,
> "chi-square" to dominate (notably if we do not count "χ²" as an
> alternative).
>
> Things look a bit different when I study R's sources; on one
> hand, I find all 4 forms (s.Subject); then in the "R source
> history", I see
>
>   $ svn log -c11342
>   ------------------------------------------------------------------------
>   r11342 | <....> | 2000-11-14 ...
>
>   Use `chi-squared'.
>   ------------------------------------------------------------------------
>
> which changed 16 (if I counted correctly) cases of 'chi-square' to 'chi-squared'.
>
> I have not found any R-core internal (or public) reasoning about
> that change, but had kept it in mind and often worked along that "goal".
>
> As a consequence, "statistically" speaking, much of R's own use has been
> standardized to use "chi-squared"; but as I mentioned, I still
> find all  4  variants even in "R base" package help files
> (which of course I now could quite quickly change  (using Emacs M-x grep, plus a script);
> but
>
> ... "as it is Friday" ... I'm interested to hear what others
> think, notably if you are native English (or "American" ;-)
> speaking and/or have some extra good knowledge on such
> matters...
>
> Martin Maechler
> ETH Zurich
>
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