The style guide of The American Psychological Association, or APA, is used in academic and professional writing across several disciplines including the social sciences, business and nursing. Properly citing and referencing works in APA style assures continuity; grants credibility to the author, and helps prevent incidence of plagiarism. Accurate resource dates lend relevance and validity to research and assist in cross-referencing. When dates are unavailable, however, the material can still be cited using a specific set of rules.
Citations placed within text in APA format generally consist of an author’s name and the date of publication in parenthesis for paraphrased sections, and name, date and page number for direct quotations. When no date is available, “n.d.” replaces the date, within the parenthesis as an abbreviation for “no date.” For example, an in-text article citation by a single author might appear as “In his study, Walker (1999) discovered...” Without the date, the phrase would be replaced with “In his study, Walker (n.d.) discovered...”
References pages in APA format appear at the end of a document, but before any appendices. Sources are listed alphabetically by author’s last name, followed immediately by the date, set in parenthesis. An example for an entry for a journal article would appear on the reference page as Spalding, L. (2013). Eating wisely. Yoga Journal (in italics), (254) 37-44. The same citation with no available date would read: Spalding, L. (n.d). Eating wisely. Yoga Journal (in italics), (254) 37-44.
It may be unusual for a book not to have date publication information, but it is fairly common for online sources not to have dates. The “n.d.” notation is used in these cases. Copyright dates, which often appear at the bottom of a website, are not necessarily publication dates.
While it is acceptable for a reference list for an online source to exclude a publication date, the list must provide a means for the reader to access the source used by the writer. APA requires the inclusion of the Digital Object Identifier, or DOI, number, when available. The DOI assures a consistent link to a resource. If it is not available, a retrieval notation must be included. It is only necessary to provide a retrieval date if the source is likely to change or disappear over time. However, the writer must provide an exact URL. For example: Emma, L. (n.d.). EReaders vs. books for college students. Global Post (in italics). Retrieved from http://everydaylife.globalpost.com/ereaders-vs-books-college-students-4521.html.