Styles of Referencing and Citation

Concept

APA style, from the American Psychological Association, is used in psychology, education and the social sciences. It uses author–date citation and a References list that is alphabetical, double-spaced and has a hanging indent. The current edition is the seventh (published in 2019); the sixth appeared in 2009. In a journal reference the article title is in sentence case, the journal title and volume are italicised and the DOI is given as a URL. Book titles are in sentence case and italic, and the publisher’s location is no longer included. The seventh edition lists up to twenty authors and cites works by three or more authors with et al. from the first citation.

Concept

In-text citations give the author and year: (Smith, 2020) or Smith (2020). With two authors both names are given with an ampersand inside brackets: (Smith & Jones, 2020); with three or more, use (Smith et al., 2020). A direct quotation needs a page number, (Smith, 2020, p. 15), and a quotation of fewer than forty words is put in quotation marks within the text, while one of forty words or more is set as an indented block quotation without quotation marks. A source cited through another is shown as (Smith, 2000, as cited in Jones, 2015). A work without a date uses n.d.; personal communications are cited only in the text.

Concept

The Modern Language Association style is used mainly in literature, languages and the humanities. It uses author–page in-text citation with no comma and no “p.”, for example (Smith 45), and a Works Cited list in alphabetical order with a hanging indent. The ninth edition appeared in 2021. Entries follow a template of core elements: author, title of source, title of container, other contributors, version, number, publisher, publication date and location. Titles of independent works such as books are italicised, and titles of shorter works such as articles are put in quotation marks. A block quotation is used for prose of more than four lines and is indented from the left margin.

Concept

Different disciplines prefer different styles. Chicago (the Chicago Manual of Style; the 17th edition of 2017 is widely cited and a newer edition appeared in 2024) offers a notes-and-bibliography system with footnotes or endnotes, used in history and the humanities, and an author–date system. Harvard is a generic author–date style with no single official manual, common in the UK and Australia. Vancouver uses numbers in order of first citation and is used in medicine. IEEE uses numbers in square brackets, such as [1], for engineering and computing. AMA uses superscript numbers for medical writing (11th edition, 2020). OSCOLA is the Oxford style for legal citation with footnotes. Turabian is a student adaptation of Chicago (9th edition, 2018). ACS serves chemistry.

Concept

Footnote conventions use Latin shorthand. Ibid. (ibidem) refers to the work cited in the immediately preceding note; op. cit. (opere citato) refers to a work already fully cited earlier, with the author’s name and page; loc. cit. (loco citato) refers to the same place (same page or passage) in a work already cited; idem means the same author; et al. means and others; cf. (confer) means compare; q.v. (quod vide) means which see; viz. means namely; e.g. (exempli gratia) means for example; i.e. (id est) means that is; passim means throughout; ff. means and the following pages. Modern manuals, including recent Chicago editions, discourage ibid. and op. cit. in favour of shortened citations.

Concept

A citation acknowledges a source inside the text and is matched by an entry in the reference list. A primary citation gives the original source, and a secondary citation cites a source through another. Citation indexing, pioneered by Eugene Garfield through the Science Citation Index, allows tracing who cites whom and led to the impact factor. Bibliometrics (the term is credited to Alan Pritchard, 1969) measures publications and citations, with classic laws: Lotka’s law on author productivity, Bradford’s law on scattering of articles across journals, and Zipf’s law on word frequency. Altmetrics measure online attention. Reference managers such as Zotero, Mendeley and EndNote store sources and format citations in many styles.