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Cheryl Iverson

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Supplementary Expressions.

Use parentheses to indicate supplementary explanations, identification, direction to the reader, or translation. (See also 8.3.2, Dashes, and 8.5.2, Brackets.)

A known volume of fluid (100 mL) was injected.

The differences were not significant (P > .05).

One of us (B.O.G.) saw the patient in 2006.

Asymmetry of the upper part of the rib cage (patient 5) and pseudarthrosis of the first and second ribs (patient 8) were incidental anomalies (Table 3).

Of the 761 hospitalized patients, 171 (22.5%) were infants (younger than 1 year).

In this issue of JAMA (p 1037), a successful transplant is reported.

The 3 cusps of the aortic valve (the “Mercedes-Benz sign”) were clearly shown on the echocardiogram.

If there is a close relationship between the parenthetical material and the rest of the sentence, commas are preferred to parentheses.

The hemoglobin level, although in the normal range, was lower than expected.

If the relationship in thought after the expressions namely (viz), that is (ie), and for example (eg) is incidental, use parentheses instead of commas.

He weighed the advice of several committee members (namely, Jones, Burke, and Easton) before making his proposal.

Punctuation Marks With Parentheses.

Use no punctuation before the opening parenthesis except in enumerations (see Enumerations below).

Any punctuation mark can follow a closing parenthesis, but only the 3 end marks (the period, the question mark, and the exclamation point) may precede it when the parenthetical material interrupts the sentence. If a complete sentence is contained within parentheses, it is not necessary to have punctuation within the parentheses if it would noticeably interrupt the flow of the sentence. Note that with complete sentences, the initial letter of the first word is capitalized.

The discussion on informed consent lasted 2 hours. (A final draft has yet to be written.) The discussion failed to resolve the question.

The discussion on informed consent lasted 2 hours (a final draft has yet to be written) and did not resolve the question.

After what seemed an eternity (It took 2 hours!), the discussion on informed consent ended.

When the parenthetical material includes special punctuation, such as an exclamation point or a question mark, or several statements, terminal punctuation is placed inside the closing parenthesis.

Oscar Wilde once said (When? Where? Who knows? But I read it in a book once upon a time, hence it must be true.) that “anyone who has never written a book is very learned.”3

Identifying Numbers or Letters.

When an item identified by letter or number is referred to later by that letter or number only, enclose the letter or number in parentheses.

You then follow (3), (5), and (6) to solve the puzzle.

If the category name is used instead, parentheses may be dropped.

Steps 1, 2, and 3 must be done slowly.


For division of a short enumeration that is run in and indicated by numerals or lowercase italic letters, enclose the numerals or letters in parentheses. (See also 19.5, Numbers and Percentages, Enumerations.)

The patient is to bring (1) all pill bottles, (2) past medical records, and (3) our questionnaire to the first office visit.

References in Text.

Use parentheses to enclose all or part of a reference given in the text. (See also 3.3, References, References Given in Text.)

Two cases of invasive zygomycosis with a fatal outcome were reported in the Archives of Dermatology (2005;141[10]:1211-1213).

In Legends.

In legends, use parentheses to identify a case or patient and parts of a composite figure when appropriate. (See also 4.2.7, Visual Presentation of Data, Figures, Titles, Legends, and Labels.)

Figure 6. Facial paralysis on the right side (patient 3).

Figure 2. Fracture of the left femur (patient 7).

The date, if given, is similarly enclosed.

Figure 2. Fracture of the left femur (patient 7, October 23, 2004).

For photomicrographs, give the magnification and the stain, if relevant, in parentheses (see also 4.2.7, Visual Presentation of Data, Figures, Titles, Legends, and Labels).

Figure 3. Marrow aspiration 14 weeks after transplantation (Wright stain, original magnification ×600).

Trade Names.

If there is a reason to provide a trade name for a drug or for equipment, enclose the trade name in parentheses immediately after the first use of the nonproprietary name in the text and in the abstract. (See also 15.4.3, Nomenclature, Drugs, Proprietary Names; and 15.5, Nomenclature, Equipment, Devices, and Reagents.)

Treatment included oral administration of indomethacin (Indocin), 25 mg 3 times a day.


If used in the text, specialized abbreviations (as specified in 14.11, Abbreviations, Clinical, Technical, and Other Common Terms) are enclosed in parentheses immediately after first mention of the term, which is spelled out in full.

Explanatory Notes.

Explanatory notes, when incorporated into the text, are placed within parentheses. In such instances, terminal punctuation is used before the closing parenthesis, the sentence(s) within the parentheses being a complete thought but only parenthetical to the text.

Parenthetical Expressions Within a Parenthetical Expression.

These are enclosed in brackets.

(Antirejection therapy included parenteral antithymocyte globulin [ATGAM], at a dosage of 15 mg/kg per day.)

But: In mathematical expressions, parentheses are placed inside brackets. See 8.5.2, Brackets, Within Parentheses.

Parenthetical Plurals.

Parentheses are sometimes used around the letters s or es to express the possibility of a plural when singular or plural could be meant. (See also 7.8.4, Grammar, Subject-Verb Agreement, Parenthetical Plurals.)

The name(s) of the editor(s) of the book in reference 2 is unknown.

Note: If this construction is used, the verb should be singular, because the s is parenthetical. In general, try to avoid this construction and use the plural noun instead or rephrase the sentence:

We do not know the name(s) of the editor(s) of the book in reference 2.

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