expressing numbers in text

 

prelude

The rules for writing numbers vary by academic discipline. While numbers are not a special focus in standard prose, they are in technical, scientific, or medical texts. Numbers written as numerals emphasize quantity more clearly than numbers spelled out as words. Overall, however, as the CBS Manual points out,

« guidelines for representing numbers may occasionally collide with the realities of some documents. When common sense or editorial judgment says a guideline is a poor choice for a specific document, follow sense or judgment. […] choose the form that is best suited for your document and follow that form as consistently as is reasonable. »

Having said this, here are the guidelines I generally follow—most of which derive from the CBE Manual.

 

NUMERALS OR WORDS

In scientific text, use arabic numerals in preference of words when the number stands for anything that can be counted. By the way, numerals are the symbols used to represent numbers. For example, there are 10 arabic numerals, i.e., 0 to 9.

Examples:
3 assays
2 hypotheses
120 samples

Note:
For non-technical texts, the Chicago Manual suggests to spell out all numbers from one through one hundred. It does, however, also give an alternative rule that applies to scientific or journalistic contexts, i.e., that of spelling out single-digit numbers and using numerals for all others.

Example:
Twenty-two kids and seven dogs were packed into two vans.
The property is held on a ninety-nine-year lease.
The house I live in is 112 years old.

Yet other scientific style guides recommend that cardinal numbers up to 12 should be written in words, except when telling the time.

Examples:
We need eight chairs and two tables.
She has four brothers.
The bus leaves at 10 am.

Spelling out single-digit numbers or numbers up to 12 appear to be rather arbitrary rules, which is why I prefer using numerals across the board.

Arabic numerals should also be used in ordinal numbers. The letters in ordinal numbers should not appear as superscripts.

Examples:
2nd        3rd        77th

Note:
The recommendation of the AMA Manual diverges from that of the CBS Manual, stating that the “numerical expression of commonly used ordinals (1st, 2nd, 3rd, 4th, etc) may appear jarring and interrupt the flow of the text. For this reason, the ordinals first through ninth are spelled out.”

Example:
The seventh patient enrolled was still relapse-free when the oncologist performed his analysis.

However, according to the AMA Manual, if a sentence contains 2 or more ordinals and at least 1 is greater than ninth, all ordinals should be expressed in numeric form.

Example:
The 5th and 12th patients experienced disease progression.

Other style guides recommend that all ordinal numbers be written in words (e.g., second, third, seventy-seventh), while yet others require ordinal numbers up to twelfth be written in words, except in dates.

Examples:
He finished third.
She was born on 9th October.

One exception to the use of numerals is that they are not used to begin a sentence. Here, the solution is to spell out the number, reword the sentence, or join the sentence to the preceding sentence.

Examples:
Twenty milligrams is the desired amount, but 15 mg is enough.
The desired amount is 20 mg, but 15 mg is enough.

The 2nd exception is when 2 numeric expressions are adjacent in a sentence. In these cases, the number easiest to express in words should be spelled out.

Examples:
The sample was divided into four 20-g aliquots.
The sample was divided into 4 aliquotes of 20 g each.
I use two 32-inch monitors side by side.

 

FORMATTING NUMBERS

In numbers of 2 to 4 digits, the numerals are run together, i.e., no extra spaces are used.

Examples:
35        789        1200        5486

In numbers of more than 4 digits, British and American English mark off groups of 3 digits with commas. The European convention (ISO 1992a) is to separate groups of 3 digits with periods.

Examples:
5,450,000      60,780,000      [British and American]
5.450.000      60.780.000      [European]

Whereas British and American English uses decimal points, European convention uses decimal commas.

Examples:
5.4      7.9      [British and American]
5,4      7,9      [European]

In decimal numbers smaller than 1.0, an initial zero (0) before the decimal point (or comma) should always be used.

Examples:
0.75
p = 0.05

 

RANGES OF NUMBERS

When writing ranges of numbers in text, the word “through” or “to” should be used to connect them.

Example:
Samples 6 through 10 were reacted in a similar manner but at approximately 100°C.

When the ranges are numbers of several digits, no digits from the 2nd number in the range should be omitted.

Example:
1938 through 1942
[not “1938–42”]

If a range of values begins a sentence, both numbers in the range, the span word, and the units are spelled out.

Example:
One hundred thirty to one hundred eighty grams per liter is the hemoglobin reference range for men.
[not “One hundred thirty to 180 g/L is the hemoglobin reference range for men.”)

Ranges of numbers and their accompanying units are expressed with a single unit symbol following the 2nd number of the range, except when the symbol is set close without spacing.

Examples:
20 to 30 kg
120 to 130 km/h
10% to 100%

 

PERCENTAGES

In scientific writing, percentages are expressed using numerals and the percent sign (%), with no space between them.

Examples:
The success rate was 95%.
The equivalence margin ranged from –15% to +15%.

If the percentage starts a sentence, both the number and “percent” are spelled out.

Example:
Twenty-five percent of the samples were positive. 

 

References

• Scientific Style and Format. The CBE Manual for Authors, Editors, and Publishers (6th edition)
• AMA Manual of Style. A Guide for Authors and Editors (11th edition)
• The Chicago Manual of Style (17th edition)