The American Psychological Association developed their documentation format for publications in the sciences, social sciences, business and nursing to not only create consistency among papers and publications but also acknowledge what phrases and ideas come from outside sources. As explained in the sixth edition of the "Publication Manual of the American Psychological Association," citations may appear at the end of borrowed material or in a signal phrase.
At the End
Parenthetical citations in APA style often appear at the end of sentences to indicate quoted or paraphrased information. They typically consist of the author's last name and the year of publication. Place the citation before the period at the end of the borrowed information but after quotation marks in a direct quote, as in this example:
"The decision belongs to the director alone" (Smith, 2012).
This structure works particularly well with quotes since the citation at the end clearly indicates which words appeared in the original.
Signal phrases at the start of borrowed material emphasize that the information comes from an outside source and therefore appear more often in APA papers. A signal phrase usually gives the author's name. Indicate the publication date in parentheses immediately after the name, as in this example:
According to Smith (2012), "the decision belongs to the director alone."
In APA style, signal phrases employing verbs should use past tense such as "noted," "acknowledged" and "explained."