Cite an article or book with a single author using the author-date method of citation. If you refer both to the author and date of publication in the text, there is no need to cite them in parentheses. For example: In 2003, Kessler showed that...
Enclose the year in parentheses if you use the author's name directly in the text. For example: Kessler (2003) found that among epidemiological samples...
Enclose both the author's name and the year of publication in parentheses if you are referencing the research in the text but are not naming the author or the publication date directly. For example: A recent study of epidemiological samples found that... (Kessler, 2003).
Cite both authors' names in the text every time you refer to their research if the work has only two authors. Use the same formats as for a single author. If you mention the authors and the publication year in the text, use the "and" construction. As for a work with a single author, there is no need to cite anything in parentheses. If you refer to the research in the text, cite the authors and date in parentheses using the ampersand between the author names. Examples are as follows:
In 2009, Smith and Jones found...
Smith and Jones (2009) found...
Recent research suggests that... (Smith & Jones, 2009)
Cite all the authors the first time you mention their research if a work has three to five authors, but use "et al." after the first author's name in subsequent citations. For example, on first mention, you would write, "Kernis, Cornell, Sun, Berry and Harlow (1993) found..." On second mention, you would write, "Kernis et al. (1993) found..." Follow the same format as indicated for a single author.
Cite only the first author's name followed by "et al." every time you refer to a work if a work has six or more authors.