A Citation is a documentation of a source material from which evidence and other information has been taken. Citations often include bibliographic information such as author's name, title of work, date of publication, etc.
A citation can be created manually or through a citation reference manager. The information presented in a citation must be organized according to a preferred or standardized format, known as a citation style.
A Citation Style is often determined by the type or subject of a paper, journal or publication preference, workplace or institutional standards, etc. For example: in the biomedical sciences, the APA and Vancouver styles are preferred. In the Humanities, the MLA style is preferred.
Citation Styles focus on in-text citations as well as reference and bibliography lists. They may also focus on manuscript formatting and structuring, over all. This will include guidelines such as presenting evidence, statistics, charts.etc.
APA is an acronym for the American Psychological Association.
APA Style originated in 1929. Its rules and guidelines--designed for clarity of identifying information and ease of access to information--are cataloged in Publication Manual of the American Psychological Association, a frequently updated guidebook used by students, professionals and editors alike.
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There are two types of referencing used in The Chicago Style Guide: 1). Notes and Bibliography and 2). Author-Date.
The notes and bibliography system is preferred by many working in the humanities—including literature, history, and the arts. In this system, sources are cited in numbered footnotes or endnotes.
The author-date system is more common in the sciences and social sciences. In this system, sources are briefly cited in the text, usually in parentheses, by author’s last name and year of publication. Each in-text citation matches up with an entry in a reference list, where full bibliographic information is provided.
For more on the Chicago Style: https://www.chicagomanualofstyle.org/tools_citationguide.html
The Council of Science Editors (CSE), formerly known as the Council of Biology Editors (CBE), use in-text citations in the name-year format. The bibliography lists the sources alphabetically at the end of the research paper.
Here is an example of the name-year format:
(McMillan et al., 2008).
The Modern Language Association (MLA) is among the most common formatting style. It is often the preferred standard for the Humanities and social sciences.
In-text citation follows the author-page format.
The Vancouver Style is formally known as Recommendations for the Conduct, Reporting, Editing and Publication of Scholarly Work in Medical Journals (ICMJE Recommendations). It was developed in Vancouver in 1978 by editors of medical journals and well over 1,000 medical journals (including ICMJE members BMJ, CMAJ, JAMA & NEJM) use this style.