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APA Style Guide: Brackets vs. Parentheses

A guide to help users create citations using APA (American Psychological Association) style.

Parentheses and brackets are used to enclose and set off material from the main text. Winding highwayAlthough writers usually need only one set of parentheses or brackets at a time, for more complex material they may need an enclosure within an enclosure (referred to as a double enclosure in this post).

Four guidelines govern how to use these punctuation marks together (or not) to handle double enclosures in an APA Style paper.

1. Use brackets inside parentheses to create a double enclosure in the text. Avoid parentheses within parentheses, or nested parentheses.

  • Correct: (We also administered the Beck Depression Inventory [BDI; Beck, Steer, & Garbin, 1988], but those results are not reported here.)
  • Incorrect: (We also administered the Beck Depression Inventory (BDI; Beck, Steer, & Garbin, 1988), but those results are not reported here.)

2. Separate citations from parenthetical text with either semicolons (for parenthetical-style citations) or commas around the year (for narrative citations). Do not use a double enclosure or back-to-back parentheses.

  • Correct: Gender differences may reflect underlying continuous attributes, such as personality (e.g., communion and agency; Spence & Helmreich, 1978). These distinctions are reflected in sexually dimorphic brain structures (see Ellis et al., 2008, for recent meta-analyses).
  • Incorrect: Gender differences may reflect underlying continuous attributes, such as personality (e.g., communion and agency) (Spence & Helmreich, 1978). These distinctions are reflected in sexually dimorphic brain structures (see Ellis et al. [2008] for recent meta-analyses).

3. When a mathematical equation contains one level of enclosure, use parentheses, ( ); for two levels, add brackets outside, [( )]; for three levels, add curly brackets outside, {[( )]}.

  • Correct: Participants were asked to solve the following math problem for after completing the priming measures: 8[x + 4(2x + 1)] = 248
  • Incorrect: Participants were asked to solve the following math problem for x after completing the priming measures: 8(x + 4[2x + 1]) = 248

4. Avoid adding a level of enclosure to statistics that already contain parentheses. Instead, use commas to set off the statistics from the text.

  • Correct: The results were statistically significant, F(1, 32) = 4.37, = .045.
  • Incorrect: The results were statistically significant (F[1, 32] = 4.37, = .045).
  • Incorrect: The results were statistically significant [F(1, 32) = 4.37, = .045].

For more on how these punctuation  marks are used, see Publication Manual §4.09, §4.10, and §4.47. Keep an eye out for more Punctuation Junction posts coming soon!

***

Example text in Guideline 2 adapted from “Men and Women Are From Earth: Examining the Latent Structure of Gender,” by B. J. Carothers and H. T. Reis, 2013, Journal of Personality and Social Psychology, 104, p. 386. Copyright 2013 by the American Psychological Association.


Lee, C. (2013, May 3,). Punctuation junction: Parentheses and brackets. Retrieved from http://blog.apastyle.org/apastyle/2013/05/punctuation-junction-parentheses-and-brackets.html

Brackets

Use brackets

to enclose the values that are the limits of a confidence interval.

  • Example: 
    95% CIs [-7.2, 4.3], [9.2, 12.4], and [-1.2, -0.5]

to enclose parenthetical material that is already within parentheses.

  • Example: 
    (The results for the control group [n = 8] are also presented in Figure 2.)

to enclose material inserted in a quotation by some person other than the original writer.

  • Example: 
    "when [his own and others'] behaviors were studied" (Hanisch, 1992, p. 24)

to include nonroutine information in a reference

  • Example: 
    Van Nuys, D. (Producer). (2007, December 19). Shrink rap radio [Audio podcast]. 
         Retrieved from http://www.shrinkrapradio.com

Exceptions

Exception 1: Do not use brackets if the material can be set off easily with commas without confounding meaning:

  • Correct: (as Imai, 1990, later concluded)
  • Incorrect: (as Imai [1990] later concluded)

Exception 2: In mathematical material, the placement of brackets and parentheses is reversed; that is, parentheses appear within brackets.

(adapted from the sixth edition of the APA Publication Manual, © 2010)

Glancing through the references examples on pages 193–215 of the APA Publication Manual, you may notice that some references include information in brackets. These brackets always appear immediately following the title element (and any of its parenthetical information). Understanding this element of an APA Style reference can give you great flexibility when creating references. 

As indicated on page 186, “nonroutine” information can be included in brackets. Fourteen of the most common notations are included on that page (including “Audio podcast,” “Data file,” “Computer software,” and others). But these are not the only possible notations.  Any information that is “important for identification and retrieval” may be included in brackets. 

This is useful when you need to clarify the type of source. For example, although Example 50 (p. 210) shows “[Audio podcast]” after the title element, “[Video podcast]” is another possibility. Likewise, in Example 53 (“Map retrieved online”) brackets are included to clarify that the title element refers to a “[Demographic map].” 

Brackets can also be used to indicate that the title element refers to more than one thing, as in Example 57, where “Eyelink II” refers to both the “[Apparatus and software].” 

In short, if you’re referencing an unusual item, consider using brackets to clarify. 


McAdoo, T. (2010, February 4,). Using brackets in APA style references. Retrieved from http://blog.apastyle.org/apastyle/2010/02/the-generic-reference-using-brackets.html

Acronyms

Using Acronyms 

  • First use: (American Psychological Association [APA], 2009)
  • Subsequent use: (APA, 2009)

The corresponding reference list entry should contain the author’s full name, not the acronym.

  • Correct: American Psychological Association. (2009).
  • Incorrect: American Psychological Association (APA). (2009).
  • Incorrect: APA. 2009.

Parentheses

Use parentheses

to set off structurally independent elements

Examples:

  • The patterns were significant (see Figure 5).
  • (When a complete sentence is enclosed in parentheses, place punctuation in the sentence inside the parentheses, like this.)
  • If only part of a sentence is enclosed in parentheses (like this), place punctuation outside the parentheses (like this).

to set off letters that identify items in a series within a sentence or paragraph (see also section 3.04 on seriation)

  • Example: 
    The subject areas included (a) synonyms associated with cultural interactions, (b) descriptors for ethnic group membership, and (c) psychological symptoms and outcomes associated with bicultural adaptation.

to group mathematical expressions (see also sections 4.09 and 4.48 in the Publication Manual)

  • Example: 
    (k – 1)/(g – 2)

to enclose numbers that identify displayed formulas and equations

  • Example: 
    Mj = αMj–1 + fj + gj * gj' (1)

to enclose statistical values

  • Example: 
    was statistically significant (p = .031)

(adapted from the sixth edition of the APA Publication Manual, © 2010)

Parentheses typically enclose extra information: either citations, which provide source details readers may or may not need or act on, or an extra thought or illustrative idea that did not warrant full elaboration in the text. As helpful as information in parentheses can be, it also is an interruption to the regular text, so keeping it to the point is ideal.


To that end, here are some things that should be done in parentheses that should not be done in regular text:

  • Use an ampersand (&) in place of and in citations (and only in citations). For example, a citation for Solo and Skywalker (1977) in text would be (Solo & Skywalker, 1977) in parentheses.
  • What would be versus in text is abbreviated vs. in parentheses (e.g., the relative heights of jawas vs. ewoks), unless one is referring to court cases, in which versus is abbreviated v. (e.g., the unlawful imprisonment suit of Organa v. The Empire).
  • Other standard Latin abbreviations should also be used in parentheses rather than written out:

    e.g. for for example (e.g., the Imperial traffic stop failed to apprehend the runaway droids)
    i.e. for that is (i.e., those were the droids they were looking for)
    viz. for namely (viz., C-3PO and R2-D2)
    cf. for compare (cf. the successful apprehension of rebels during the Cloud City mission)
    etc. for and so forth (Han Solo, Princess Leia Organa, C-3PO, etc.)

Please note in the examples that commas are used with Latin abbreviations where they logically would go if the phrases were written out. To help, here is a handy printable guide to Latin phrases.

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