AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020

Hyphens and Dashes
Punctuation

Hyphens and dashes are internal punctuation marks used for linkage and clarity of expression.

8.3.1 Hyphen.

The hyphen is a connector; it may join “what is similar and also what is disjunctive . . . it divides as well as marries.”³ The hyphen connects words, prefixes, and suffixes permanently or temporarily. Certain compound words always contain hyphens. Such hyphens are called orthographic. Examples are merry-go-round, free-for-all, happy-go-lucky, and mother-in-law. For temporary connections, hyphens help prevent ambiguity, clarify meaning, and indicate word breaks at the end of a line.

In general, hyphens should be used only as an aid to the reader’s understanding, primarily to avoid ambiguity. For capitalization of hyphenated compounds in titles, subtitles, subheads, and table heads, see 10.2.2, Titles and Headings, Hyphenated Compounds.

8.3.1.1 Temporary Compounds.

Hyphenate temporary compounds according to current dictionary usage and the following rules:

Hyphenate a compound that contains a noun or an adverb (except for adverbs ending in -ly; see 8.3.1.6, When Not to Use Hyphens) and a participle that together serve as an adjective modifying the noun they precede (eg, angiotensin-converting enzyme). Do not use the hyphen if the compound follows the noun.

breast-conserving surgery

most-read work in the collection (But: The work was the most read in the collection.)

It was a placebo-controlled trial. (But: The trial was placebo controlled.)

This was a well-edited volume. (But: This volume was well edited.)

The rash was a treatment-related adverse event. (But: The adverse event was treatment related.)

Hyphenate a compound adjectival phrase when it precedes the noun it modifies but not when it follows the noun. Hyphenation before the noun helps make the relationship of the words that precede the noun clearer and easier for a reader to understand.

side-by-side placement (But: placed side by side)

Hyphenate an adjective-noun compound when it precedes and modifies another noun but not when it follows the noun. When such a compound follows the noun, the hyphenation is not required for easier understanding.

low-quality suture material (But: suture material of low quality)

highest-quality printing (But: printing of highest quality)

low-density resolution (But: resolution of low density)

high-altitude sickness (But: sickness at high altitude)

very low-birth-weight children (But: children of very low birth weight)

low-molecular-weight heparin (But: heparin of low molecular weight)

very low-density lipoprotein (But: lipoprotein of very low density)

foreign-body reaction (But: reaction to a foreign body)

total-body imaging (But: imaging of the total body)

total-breast radiation therapy (But: radiation therapy of the total breast)

Note: In most instances middle-, high-, and low- adjectival compounds are hyphenated.

For compound adjectival phrases, adverb-participle compounds, and adjective-noun compounds that have become commonplace and familiar in everyday usage, hyphenate these phrases or compounds whether they precede or follow the noun they modify.

long-term therapy

the commitment was long-term

a middle-aged man

he was already middle-aged

the left-handed participants

the participants who were left-handed

cost-effective system

a system that was cost-effective

cafeteria-style dining

the dining was cafeteria-style

However, for combinations representing colors, nouns plus adjectives, and nouns plus participles, hyphenate before but not after a noun. (Follow The Chicago Manual of Style, 17th edition, to verify.)

up-to-date vaccinations

the vaccinations were up to date

state-of-the-art equipment

equipment that was state of the art

The author provided black-and-white illustrations.

The author’s illustrations were black and white.

Hyphenate a combination of 2 or more nouns used coordinately as a unit modifier when preceding the noun but not when following.

the Binet-Simon test (But: the test of Binet and Simon)

Beer-Lambert law (But: the law of Beer and Lambert)

Charcot-Marie-Tooth disease (But: the disease described by Charcot, Marie, and Tooth)

Hosmer-Lemeshow goodness-of-fit test (But: the goodness-of-fit test of Hosmer and Lemeshow)

the patient-physician relationship (But: the relationship between the patient and the physician)

Presentation of ratios as numbers or abbreviations is an exception to this rule. In ratios presented as numbers or abbreviations, use a colon (see 8.2.3, Colon). For ratios presented as words, use the word to or, if the word combination has become accepted as a single term, such as cost-benefit analysis, a hyphen.

Hyphenate a combination of 2 or more nouns of equal participation used as a single noun (see 8.4.1, Forward Slash [Virgule, Solidus], Used to Express Equivalence or Duality).

William Carlos Williams was a physician-poet.

W. Somerset Maugham is considered a great physician-writer.

She is an obstetrician-gynecologist.

Many of JAMA’s contributors are physician-investigators.

This was a case-control study of sleep-wake problems.

The importance of having access to a cardioverter-defibrillator on the airplane was evident after this incident.

Provide the best health care for all, says the citizen-patient; but don’t allow costs to rise, says the citizen-taxpayer.

The physician-patient may become impatient with treatment.

This was a 50-50 proposition.

The kidney-ureter-bladder abdominal radiograph showed normal bowel gas patterns.

Hyphenate the initials of an author with a hyphenated name when referred to parenthetically. For example, for parenthetical reference to author Horace Pendlebury- Davenport,

One of us (H.P.-D.) . . .

Hyphenate most compound nouns that contain a preposition. Follow the latest edition of Merriam-Webster’s Collegiate Dictionary.

(But: onlooker, passerby, passersby, handout, workup, workups, makeup, upregulate, downregulate)

Hyphenate a compound in which a number is the first element and the compound precedes the noun it modifies (see 18.0, Numbers and Percentages).

18-factor blood chemistry analysis

7-fold increase

half-life

half-lives

3-dimensional (also 3-D)

2-way street

ninth-grade reading level

1-cm increments

Hyphenate 2 or more adjectives used coordinately or as conflicting terms whether they precede the noun or follow as a predicate adjective.

The false-positive test results were noted.

The test results were false-positive.

The patient was diagnosed as having relapsing-remitting multiple sclerosis.

The patient’s multiple sclerosis was diagnosed as relapsing-remitting.

The patient’s tonic-clonic seizures began in 2012.

In 2012, the patient began having seizures that were tonic-clonic.

We performed a double-blind study.

The test we used was double-blind.

Hyphenate color terms in which the 2 elements are of equal weight.

blue-gray eyes

blue-black lesions (lesions were blue-black)

bluish-gray lesions

Hyphenate compounds formed with the prefixes all-, ex-, and self- whether they precede or follow the noun.

Note: With the prefix vice, follow the latest edition of Merriam-Webster’s Collegiate Dictionary, eg, vice-chancellor, vice-consul, but vice president, vice admiral.

Hyphenate compounds that contain the suffixes -type, -elect, and -designate.

Hyphenate most contemporary adjectival cross- compounds (consult the latest edition of Merriam-Webster’s Collegiate Dictionary for absolute accuracy; there are exceptions, eg, crossbred, crosshatched, crossover, crossmatch, cross section).

Hyphenate adjectival compounds with quasi.

Most nouns that begin with quasi are not hyphenated but instead are set open (eg, quasi diplomat), although some are closed up (eg, quasicrystal, quasiparticle). Follow the latest edition of Merriam-Webster’s Collegiate Dictionary.

Hyphenate some compounds in which the first element is a possessive. Consult the latest edition of Merriam-Webster’s Collegiate Dictionary.

Hyphenate all prefixes that precede a proper noun, a capitalized word, a number, or an abbreviation.

pro-African initiatives

pre-AIDS era

post-2005 ruling

Note: There is increasing acceptance of the use of a stand-alone prefix with a hyphen in a form of ellipsis in which the prefix refers to the root of a subsequent word with an unhyphenated prefix.

We found a need for pre- and postoperative examination.

Patients were categorized as hyper- or hypotensive.

This could be an in- or outpatient procedure.

The JAMA Network journals choose not to follow this trend and instead would use the following:

We found a need for preoperative and postoperative examination.

Patients were categorized as hypertensive or hypotensive.

This could be an inpatient or outpatient procedure.

When 2 or more hyphenated compounds have a common base, omit the base in all but the last. In unhyphenated compounds written as 1 word, repeat the base.

first-, second-, and third-grade students

10- and 15-year-old boys

anterolateral and posterolateral aspects

Hyphenate compound numbers from 21 to 99 (cardinal and ordinal) when written out, as at the beginning of a sentence (see 18.1, Use of Numerals).

Thirty-six patients were examined.

Twenty-fifth through 75th percentile rankings were shown.

One hundred thirty-two people were injured in the plane crash.

Hyphenate fractions used as nouns or adjectives.

Three-fourths of the questionnaires were returned.

A two-thirds majority was needed.

The flask was three-fourths full.

8.3.1.2 Clarity.

Use hyphens to avoid ambiguity. If a term could be misleading without a hyphen, hyphenate it. As with the use of commas to indicate pauses, the use of the hyphen to provide clarity may be subjective. What is clear to one person may be a source of ambiguity to another. Use the following guidelines and a healthy dose of common sense.

a small-bowel constriction (constriction of the small bowel)

a small bowel constriction (a small constriction of the bowel)

a single-specialty center (a center devoted to a single specialty)

a single specialty center (1 center devoted to a specialty)

a large-bowel resection (resection of the large bowel) (Better: a colon resection)

a large bowel resection (a large resection of the bowel)

a solid-organ transplant program (a program for transplant of solid organs)

a solid organ transplant program (a program for organ transplant that is solid, ie, well established) (Better: a well-established transplant program)

It would be tough to conceive of a better smelling “machine” than a dog (dogs have a high ability to sniff out bombs).

It would be tough to conceive of a better-smelling “machine” than a dog (dogs have a pleasing aroma).

Use a hyphen after a prefix when the unhyphenated word would have a different meaning.

Note: Do not hyphenate other forms of these words for which no ambiguity exists (eg, retreatment, recreational).

Occasionally, a hyphen is used after a prefix or before a suffix to avoid an awkward combination of letters, such as 2 of the same vowel or 3 of the same consonant (with exceptions noted in 8.3.1.6, When Not to Use Hyphens). Follow the latest edition of Merriam-Webster’s Collegiate Dictionary or Dorland’s or Stedman’s medical dictionaries.

(Some exceptions to this rule include microorganism, cooperation, reenter [see 8.3.1.6, When Not to Use Hyphens].)

In complex modifying phrases that include suffixes or prefixes, combinations of hyphens and en dashes are sometimes used to avoid ambiguity (see 8.3.2.2, En Dash).

8.3.1.3 Expressing Ranges and Dimensions.

When expressing ranges or dimensions used as modifiers, use hyphens and spacing in accordance with the following examples in the left-hand column. The alternatives in the right-hand column show how to express dimensions when not used as modifiers.

In the text, do not use hyphens to express ranges (see 18.4, Use of Digit Spans and Hyphens).

The adverse events were experienced by 5% to 10% of the group.

Hyphens are, however, used for (1) ranges expressing fiscal years, academic years, life spans, or study spans, (2) ranges given in parentheses, and (3) in figures and tables.

In subsequent national surveys, the prevalence of diabetes in the Chinese population was 2.5% in the 1994 survey and 5.5% in the 2000-2001 survey.

The patients’ median age was 56 years (range, 31-92 years).

Note that no hyphens are needed in cases of the following type:

a case of mild to moderate hypertension

the waist to hip ratio

the cup to disc ratio

Do not use a hyphen to express ranges, even within parentheses or in a table, if one of the values in the span includes a minus sign (see 18.4, Use of Digit Spans and Hyphens).

Change in body weight was −4.0 kg (95% CI, −5.8 to −2.3 kg).

8.3.1.4 Word Division.

Use hyphens to indicate division of a word at the end of a line (follow the latest edition of Merriam-Webster’s Collegiate Dictionary or Dorland’s or Stedman’s medical dictionaries).

8.3.1.5 Division of URLs, Email Addresses, Karyotypes, Long Formulas.

Do not add a hyphen to URLs or email addresses that break at the end of a line.

For guidance on breaking long karyotypes, see 14.6.4.3.3, Human Chromosomes, Chromosome Rearrangements, Punctuation. For guidance on breaking long formulas, see 20.4, Long Formulas.

8.3.1.6 When Not to Use Hyphens.

Rules also exist for when not to use hyphens.

The following common prefixes are not joined by hyphens except when they precede a proper noun, or an abbreviation: ante-, anti-, auto-, bi-, co-, contra-, counter-, de-, e-, eco-, extra-, infra-, inter-, intra-, micro-, mid-, multi-, non-, over-, pre-, post-, pro-, pseudo-, re-, semi-, sub-, super-, supra-, trans-, tri-, ultra-, un-, under- (but see also 8.3.1.2, Punctuation, Hyphens and Dashes, Hyphen, Clarity). Note that email is treated as one word, without a hyphen. However, other words preceded by e- (eg, e-cigarette, e-commerce, e-prescribing, e-print) retain the hyphen.

Retain the hyphen if needed to avoid ambiguity or awkward spelling that could interfere with readability: co-opt, co-payment, co-twin, intra-aortic, non-breastfeeding.

Retain the hyphen when the term after the prefixes anti-, neo-, pre-, post-, and mid- is a proper noun or a number (see 8.3.1.1, Hyphen, Temporary Compounds), eg, mid-1900s, mid-Atlantic crossing.

The following suffixes are joined without a hyphen, with exceptions if the clarity would be obscured (see 8.3.1.1, Hyphen, Temporary Compounds): -hood, -less, -like, -wise.

The suffix -wide is usually closed up (worldwide, citywide) unless it follows a proper noun (Chicago-wide) or a word of 3 or more syllables (university-wide). Editorial discretion may also dictate a hyphen in less common combinations to enhance readability (genome-wide association studies, hospital-wide implementation).

Some combinations of words are commonly read together as a unit. As such combinations come into common use, the hyphen tends to be omitted without a sacrifice of clarity. Use the latest editions of Merriam-Webster’s Collegiate Dictionary and Dorland’s and Stedman’s medical dictionaries as guides to common usage (eg, broad-spectrum antibiotics is hyphenated in Dorland’s; open heart surgery, deep venous thrombosis, and small cell carcinoma are not). For terms not found in these sources, use a reader’s perspective and the context as guides. When no confusion is likely, leave open. If there is a possibility of confusion, hyphenate. A short list of examples that can usually be presented without hyphens is given here.

Do not hyphenate names of disease entities used as modifiers.

Do not use a hyphen after an adverb that ends in -ly even when used in a compound modifier preceding the word modified; in these cases, ambiguity is unlikely and the hyphen can be dispensed with.

Note: Do hyphenate terms such as early-onset Alzheimer disease. (Early merely happens to end in ly but is not an adverb created from another word.)

Do not hyphenate names of chemical compounds used as adjectives.

carbon dioxide laser

sodium chloride solution

tannic acid test

Most combinations of proper adjectives derived from geographic entities are not hyphenated when used as noun or adjective formations.

(But: Scotch-Irish ancestry. Here the hyphen is used to indicate descent from Scottish settlers in Northern Ireland. Also sub-Saharan Africa. Here the hyphen connects the prefix sub- to the adjective Saharan.)

Do not hyphenate Latin expressions or non—English-language phrases used in an adjectival sense. Most of these are treated as separate words; a few are joined without a hyphen. Follow the latest edition of Merriam-Webster’s Collegiate Dictionary.

Note that when post is used as a combining adjectival form, as in postmortem examination, it is set closed up. When it is used as an adverb, as in post hoc testing, it is set as 2 separate words. This distinction is apparent in the examples below:

postpartum depression

depression that occurs post partum

Do not hyphenate modifiers in which a letter or number is the second element.

grade A eggs

study 1 protocol

type 1 diabetes

phase 2 study

8.3.1.7 Compound Official Titles.

Hyphenate combination positions of office but not compound designations as follows:

secretary-treasurer

acting secretary

honorary chair

editor in chief

(But: past vice president, executive vice president, past president)

For then, hyphenate and capitalize as in these examples.

This policy was enacted under the then-president.

This policy was enacted under then-President Obama.

8.3.1.8 Special Combinations.

Special combinations may or may not need the use of hyphens. Consult Dorland’s or Stedman’s medical dictionaries and the latest edition of Merriam-Webster’s Collegiate Dictionary. Note that they may not always agree, and in these cases, a publication will need to indicate a preference to ensure internal consistency (see 14.0, Nomenclature, and 16.0, Greek Letters).

8.3.2 Dashes.

Dashes, another form of internal punctuation, convey a particular meaning or emphasize and clarify a certain section of material within a sentence. Compared with parentheses, dashes may convey a less formal or more emphatic “aside.”

There are 4 types of dashes, which differ in length: the em dash (the most common), the en dash, the 2-em dash, and the 3-em dash.

8.3.2.1 Em Dash.

Em dashes are used to indicate a marked or pronounced interruption or break in thought. It is best to use this mode sparingly; do not use an em dash when another punctuation mark (for instance, the comma or the colon) will suffice or to imply namely, that is, or in other words, when an explanation follows.

He was young—in his early 50s—with a body ravaged by an incurable, highly aggressive prostate cancer.

The Amarin decision—if it is neither modified nor reversed—may well put patients, and the evidence base for medical practice, at risk.

An em dash may be used to separate a referent from the subject of a clause that follows or precedes:

Osler, Billings, Apgar—these were the physicians she tried to emulate.

Direct-to-consumer laboratories have allowed patients to bypass the health care establishment, opening a door to our most personal data—DNA.

8.3.2.2 En Dash.

The en dash is longer than a hyphen but half the length of the em dash. The en dash shows relational distinction in a hyphenated or compound modifier, 1 element of which consists of 2 or more words or a hyphenated word, or when the word being modified is a compound.

8.3.2.3 2-Em Dash.

The 2-em dash is used to indicate missing letters in a word.

The study was conducted at N—— Hospital, noted for its low autopsy rate.

8.3.2.4 3-Em Dash.

The 3-em dash is used to show 1 or more missing words.

Each participant was asked to fill in the blank in the following statement:

“I usually sleep ——— hours per day.”

I admire Dr ——— too much to expose him in this anecdote.