AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020
Use of Numerals
Numbers and Percentages
Any policy on the use of numbers in text must take into account the reader’s impression that numbers written as numerals (symbols) appear to emphasize quantity more strongly than numbers spelled out as words. Because numerals convey quantity more efficiently than spelled-out numbers, they are generally preferable in technical writing. In literary writing, by contrast, spelled-out numbers may be more compatible with style. Despite these general principles, usage may appear inconsistent when a publication chooses to use numerals in some instances and words in others. The guidelines outlined in this section attempt to reduce these inconsistencies and avoid use of numerals that may be jarring to the reader. In situations that are not governed by these guidelines, common sense and editorial judgment should prevail.
18.1 Use of Numerals.
In scientific writing, numerals are used to express numbers in most circumstances (eg, 5 not five). Exceptions are the following:
■Numbers that begin a sentence, title, subtitle, or heading (see 18.2.1, Beginning a Sentence, Title, Subtitle, or Heading)
■Common fractions (see 18.1.2, Common Fractions)
■Accepted usage, such as idiomatic expressions and numbers used as pronouns (see 18.2.2, One Used as a Pronoun)
■Other uses of one in running text (text that is not part of an equation or otherwise separated from the main body of the text)
■Ordinals first through ninth (see 18.2.4, Ordinals)
■Numbers spelled out in quotes or article titles (see 18.2, Spelling Out Numbers)
Five Voices, One Story
Preventing Infections in the Intensive Care Unit: One Size Does Not Fit All
Note the following examples of numerals in text:
The relative risk of exposed individuals was nearly 3 times that of the controls.
In the second phase of the study, 3 of the investigators administered the 5 tests to the 7 remaining participants. The test scores showed a 2- to 2.4-fold improvement over those of the first phase.
In 2 of the 17 patients in whom both ears were tested, we were unable to obtain responses from either ear. While testing patient 3, we experienced technical problems that consisted of unmanageable electrical artifacts.
Groups 1 and 2 were similar in terms of demographic and clinical characteristics (Table 1). Table 2 lists the 4 tests that were performed.
A 3-member committee from the US Food and Drug Administration visited the researchers.
18.1.1 Numbers of 4 or More Digits to Either Side of the Decimal Point.
Commas are not used in large numbers. In 4-digit numbers, the digits are set closed up. For numbers of 10 000 or greater, a thin space is used to separate every 3 digits starting from the right-most integer (or, in numbers with decimals, from the left of the decimal point). For numbers with 5 or more digits to the right of the decimal point, a thin space is used between every 3 digits starting from the right of the decimal point (see 17.4, Use of Numerals With Units).
The exact weight of the salt was 8.453 98 g, but its reported value was rounded to 8.4540 g.
Our analytical sample included all 2455 community-dwelling individuals 65 years or older, representing 32 294 810 elderly persons in the United States.
18.1.2 Common Fractions.
Common fractions are written with a numerator and denominator in which both are integers (eg, 1/3, 1/2, 7/8). Where spelled out, simple common (where the numerator and denominator are nonzero integers, eg, 9/10) and nonsimple (when the numerator or denominator contain fractions) fractions are expressed with hyphenated words, whether the fraction is used as an adjective or a noun. Mixed fractions are typically expressed in numerals (see 18.1.3, Mixed Fractions).
Of those attending, nearly three-fourths were members of the association.
There is a half-second delay before the intensive care unit alarm triggers after an arrhythmia is detected.
The institutional review board committee requires a two-thirds majority to establish a consensus when voting on ethical matters.
The orthopedic surgeon asked for a seven-eighths-inch-diameter rod.
In some cases, fractions can be expressed with an indefinite article preceding the unit. Such constructions do not use the hyphen.
The test concluded after half an hour.
A quarter may be used in place of one-fourth.
A quarter of the consensus panel dissented.
Note: In scientific reports, precision is preferred (eg, 24% instead of “a quarter”).
18.1.3 Mixed Fractions.
Mixed fractions are the combination of a whole number and a fraction into a single, mixed number. They may be used for less precise measurements instead of decimals. These expressions usually involve time. Common fractions are typically spelled out (see 18.1.2, Common Fractions).
The surgery lasted 3¼ hours.
The patient was hospitalized for 5½ days.
Of the patients returning for a second visit, half received the intervention.
White women comprise approximately half of those who use the program for breast cancer screening, one-fourth are Hispanic women, and approximately 16% are black women.
18.1.4 Measures of Time.
Measures of time usually are expressed as arabic numerals (see 13.3, Days of the Week, Months, Eras). When dates are provided, numerals should be used for day and year; the month should be spelled out unless listed in a table. Conventional form for time and dates (11:30 PM on February 25, 1961) is preferred to European or military form (2330 on 25 February 1961). However, use of military time may clarify the time course in figures that depict a 24-hour experiment, times of drug dosing, and the like. For time, if the hour of the day is given, AM or PM is used and set in small capital letters (see 21.0, Editing, Proofreading, Tagging, and Display). When referring to time on the hour, the minutes may be omitted (eg, 3 PM). With 12 o’clock, simply use noon or midnight, whichever is intended.
At 5:45 AM, October 15, 2004, the researchers completed the final experiment.
The patient was admitted to the ward service just after midnight on January 1, 2016.
When referring to a position as it would appear on a clock face, express the position by means of numerals followed by o’clock (See 8.2.3.3, Colon, Numbers).
The needle was inserted at the 9-o’clock position.
The procedure was scheduled to begin at 9 AM.
18.1.5 Measures of Temperature.
Use the degree symbol with Celsius and Fahrenheit measures of temperature but not for Kelvin.1 A space should appear between the number and the degree symbol (see 17.3.8, Spacing). Changes in temperature are expressed as higher and lower and not warmer or colder (see 18.4, Use of Digit Spans and Hyphens).
The plates were cultured at 17 °C, which was 3 °C lower than usual.
The patient was febrile (temperature, 38.8 oC).
The thermodynamic temperature equivalent to 25 oC is 298.15 K.
18.1.6 Measures of Currency.
For sums of money, use the appropriate symbol to indicate the type of currency (eg, $, €, £, ¥; see 17.5.12, Currency).1
His charge for the medication was $55.60 plus $0.95 for shipping.
The equivalent sum in euros was €30.