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

Rolf Turner r@turner @end|ng |rom @uck|@nd@@c@nz
Fri Oct 18 22:19:17 CEST 2019

```I have the vague impression that "chi-squared" is more common in British
usage and "chi-square" more common in American usage.  I'm pretty sure
that either is acceptable, although "chi-squared" sounds much better to
my ear.

Of course within a given document (or collection of related documents)
consistency is mandatory.

cheers,

Rolf

On 19/10/19 1:51 AM, Martin Maechler 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"
>
>
>> 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'.
>
> 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...

```