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MATH 317 Statistics and Research Methods Laboratory

Purdue Online Writing Lab

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The Online Writing Lab (OWL) at Purdue University houses writing resources and instructional material as a free service of the Writing Lab at Purdue. Students, members of the community, and users worldwide are welcome to use OWL for information to assist with writing projects. 

OWL has extensive examples, explanations and tutorials on all citation styles, including APA, MLA and Chicago.  If you have a citation question, it's almost certain you'll find your answer on OWL.

APA Citations

MLA Citations

Harvard Style

The Harvard referencing system is known as the Author-Date style. It emphasizes the name of the creator of a piece of information and the date of publication. There is no single, definitive version of the Harvard style. 

The following examples are derived from the professor's guidelines. Always refer to the professor's instructions for citations.


In text with alphabetical Literature Cited:

Single author = (Vandergon, 2001); Two authors = (Vandergon and Riggs, 1999); Three+ authors = (Vandergon et al., 2008)


  • Citric acid has been found to inhibit browning in apples (Jones and Smith, 2013). 
  • Jones and Smith (2013) found that addition of citric acid leads to inhibition of browning in apples.

Please note that authors (see above) AND publication date are necessary, BUT no other information, including page numbers are necessary.


In text with numbered references Literature Cited:

References are numbered in order of appearance 1,2,3 etc.


  • Citric acid has been found to inhibit browning in apples.1 or [1]  
  • Citric acid has been found to inhibit browning in apples [1].

Please note that references are then listed in the Literature cited section in a numbered format from the first to last appearance in text, NOT alphabetically.


Proper Citation format for References or Literature Cited:

Must include: Authors, Title (of article or book chapter), Journal (or book title), Year published, Volume (if journal or series book), page numbers. DOI numbers are OK to add, BUT URLs for your access are NOT sufficient.

Please note that URLs are OK for web sources – but these are rarely authoritative scientific sources and should be avoided.

Example Book:

  • Irmscher, Christoph. Louis Agassiz: creator of American science. Houghton Mifflin Harcourt, 2013

Example Book Chapter:

  • Lilly Vámos-Vigyázó, Prevention of Enzymatic Browning in Fruits and Vegetables Enzymatic Browning and Its Prevention. Chapter 4. May 5, 1995, p. 49-62 DOI:10.1021/bk-1995-0600.ch004

Example Journal Citations:

  • Gabriela Rapeanu, Ann Van Loey, Chantal Smout, Marc Hendrickx, Biochemical characterization and process stability of polyphenoloxidase extracted from Victoria grape (Vitis vinifera ssp. Sativa), In Food Chemistry, Volume 94, Issue 2, 2006, Pages 253-261, ISSN 0308-8146,
  • Chang-Kui Ding,Kazuo Chachin,*, Yoshinori Ueda, and, and Yoshihiro Imahori, Purification and Properties of Polyphenol Oxidase from Loquat Fruit, Journal of Agricultural and Food Chemistry 1998 46 (10), 4144-4149 DOI: 10.1021/jf980093s

Citation Management System - Zotero