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I am from Europe and always use a comma as a decimal separator. Thus, in all previous publications I have used a comma as a separator, noone ever objected. We recently submitted a new manuscript and one reviewer comment we got was that we should use points instead of commas as separators. The article was written in English; the journal has a style guide but the separator issue is not covered.

Personally, I think this request is weird, as both versions are widely used and not, like non-SI units limited to very few countries. Also, I don't think that anyone will mistake 2,34 mm as anything other than what it is supposed to mean, even if they would rather write 2.34 mm instead.

So my question is: is there an (unwritten) rule about that point instead of commas should be used as separators in academia that I don't know about or is the reviewer simply trying to change the data formatting to their own preference?

Massimo Ortolano
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Sursula
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  • The extended discussion about the usage of commas or points as decimal separators has been moved to chat. Please, if you have a compelling reason for either of the two choices, post it as an answer, and read this FAQ before posting another comment. – Massimo Ortolano Sep 18 '22 at 13:46

4 Answers4

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(You did not specify the language of the paper, so I am going to assume that it is written in English.)

There is no rule that in academia points must be used instead of commas.

There is, however, a rule that in English the point rather than the comma is used. If you are writing your paper in English, then you should use the point, for exactly the same reasons that you should write quotations "like this" instead of writing them «like this». (More precisely, this seems to hold in every variety of English except for South African English.)

The fact that you feel inclined to use the comma rather than the point is more a question of you importing the conventions of your own language into English, not a clash between your personal preference and the referee's. It's not substantially different from a French person being inclined to write quotations «like this» or a German person being inclined to write "I think, that this is true" with the extra comma.

Of course, this works both ways. If you are writing a paper in German or Turkish, then you should use the decimal comma.

(Beware that I do not work in a field where decimal separators are used on a regular basis, though.)

Adam Přenosil
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  • I'm not entirely sure but I think in British English one would use a comma and not a point as a decimal separator. So the question for a non-English speaker is not of importing conventions of their native language but rather of chosing between British and American English conventions. – quarague Sep 15 '22 at 12:27
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    My understanding is that British English also uses the decimal point. Either way, my point is: decide what your target language is and then write in that language and follow its typographic conventions. "I am from Europe and always use the comma as a decimal separator" is not a relevant reason to prefer the decimal comma to the decimal point. The OP more or less explicitly says that they use the decimal comma because it is what they are used to from their own language. – Adam Přenosil Sep 15 '22 at 12:36
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    I just glanced at an issue of Philosophical Transactions, and they clearly use a decimal point, not a comma. When preparing papers in the past for other British English publishers, it was always a decimal point for them as well. Regardless of how numbers are written by the general public, the decimal point is used in technical journals even on the East side of the Atlantic. – Jon Custer Sep 15 '22 at 13:06
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    British English exclusively uses a decimal point. The historic difference between BrE and AmE here was that BrE used to prefer a raised decimal point (interpunct), but it's always been a point rather than a comma. – Especially Lime Sep 15 '22 at 14:08
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    I believe that the English speaking world all uses the decimal point (the US, the UK, Canada (except Quebec), Australia and New Zealand all use points rather than commas). Weirdly, they also use "L" rather than a script l for liter/litre. – Flydog57 Sep 15 '22 at 19:50
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    Actually, "like this" uses simple quotation marks, which are generic simplified symbols for easier input, though not suitable for printing. The proper equivalent of «like this» is “like this” (for English), „like this” (for Polish), „like this“ (for German) etc. – MrVocabulary Sep 15 '22 at 20:11
  • I have edited the answer to reflect the comments. @MrVocabulary Your comment is entirely correct as far as printed text goes, but since "..." is almost universally used online instead of “...“, I will let it stand. – Adam Přenosil Sep 15 '22 at 20:47
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    @Flydog57 L or l is the official symbol (p. 124). ℓ is apparently an affectation used to distinguish between l and 1, even though the official symbol is L. – chrylis -cautiouslyoptimistic- Sep 15 '22 at 20:49
  • The SI recognizes both l and L (but not the script l, it turns out). You you can measure the water for your bread recipe as either 500 ml or 500 mL. In general, English speaking countries use L while everyone else uses l – Flydog57 Sep 15 '22 at 21:24
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    @Flydog57 I'm in the UK and don't remember ever seeing mL. Looking in cupboards, everything given in millilitres uses "ml", although larger items just say "litre(s)" rather than abbreviating. Presumably this is an AmE/BrE difference. – Especially Lime Sep 16 '22 at 05:54
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    @quarague As an added note: I am not a native speaker, and during my English education (and other instances that have contributed to me learning the language), I have been "exposed" to both american and british English as well as other forms of English. I would not be able to confidently say that what I am writing is any specific form of English, but rather "English". I guess this applie to many other non-native speakers and thus a rule for English in general is usefull. – Sursula Sep 16 '22 at 06:46
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    @Flydog57 You really only ever should use L, because l is an objectively terrible symbol and it baffles me that it's still allowed. Demonstration in three keystrokes: 1lI. – AmiralPatate Sep 16 '22 at 07:24
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    @EspeciallyLime, I agree, lower-case l is normal in the UK for litres. But it's not universal (checking my lunchtime shopping) - I have a 1L carton of milk here. – Chris H Sep 16 '22 at 13:56
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    What the BIPM SI brochure (linked by @chrylis-cautiouslyoptimistic- above) actually says is that, according to the usual algorithm for deciding the case of unit symbols, "litres" should be "l", but "L" is also permitted as a concession to the fact that, in some fonts, "l" is difficult to distinguish from "1". – Daniel Hatton Sep 16 '22 at 22:08
  • A reference for comma before "that". – Peter Mortensen Sep 17 '22 at 10:10
  • Re "a German person being inclined to write "I think, that this is true" with the extra comma": In Danish as well (though I think the difference in English is taught). But I also see it a lot by users from India (same language roots or misguided text books?). – Peter Mortensen Sep 17 '22 at 10:18
  • @AmiralPatate Yeah, sometimes I'll copy and paste a character into Google just to see whether it's a capital I or lower case l (this is also an argument against sans serif fonts). – Acccumulation Sep 18 '22 at 02:27
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The ISO 80000-1:2013 standard allows the use of either "." or "," as a decimal point, but not a mixture of the two in the same document. It also says one should never use either of them as a thousands separator (the correct character to use as a thousands separator being a thin space).

Daniel Hatton
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    "It also says one should never use either of them as a thousands separator". Excellent! I hate coming across a number (e.g. "1,234" or "3.456") and having to look for context in order to understand if it really means 1234 or 1 + 234 / 1000. – Eric Duminil Sep 16 '22 at 13:07
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    A number of programming languages have started to allow 1_234 as an unambiguous thousands separator which I quite like. – Oscar Smith Sep 16 '22 at 20:48
  • Yes, @OscarSmith, but it should be noted in the context of this question that in the cases I know, that's as opposed to not allowing any thousands separator at all. And (in source code) having standardized on the decimal point as a decimal separator. No doubt the latter reflects the influence of English-speaking practitioners on the development of early programming languages. – John Bollinger Sep 16 '22 at 20:51
  • @OscarSmith and JohnBollinger As I read the POSIX standard, POSIX-compliant languages should allow both the thousands separator and the decimal point character to be configured via LC_NUMERIC. – Daniel Hatton Sep 18 '22 at 19:30
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In American, British, and Canadian English, the decimal separator should be a point, not a comma. The Chicago Manual of Styles says the decimal point is represented by a comma in European countries except Great Britain (16th edition, rule 9.20). The trouble is that in US and British English, a comma is used to separate groups of three digits (e.g., 12,345.00), and therefore it should not also be used as a decimal separator. Not being able to unambiguously interpret 37,012 would be a major snafu.

The Chicago Manual of Style is followed by a great many publishing houses. It also says (rule 9.56) that in SI units, "thin, fixed spaces rather than commas are used to mark off groups of three digits", which removes the ambiguity I just pointed out. Nevertheless, the rule is clear, and US undergraduate students correct me if I use the wrong symbol for a decimal separator.

Norbert S
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If the journal has no preference mentioned then I would stick with the customary one for the country of the journal. Much like you would use British-English for UK publications and American-English for USA ones (unless otherwise stated).

Rob
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    I'm not sure this is a good rule for English-language journals published from countries where English is not the official language. As far as I can tell, these quite often adopt the normal English style i.e. decimal point as separator, even when the convention in their country is for a comma. – GB supports the mod strike Sep 16 '22 at 02:15