What is a DOI? A DOI (digital object identifier) is a unique alphanumeric string assigned by a registration agency (the International DOI Foundation) to identify content and provide a persistent link to its location on the internet.
NOTE: It is regarded as the most important part of the citation because it will accurately direct users to the specific article.
Think of it as a "digital fingerprint" or an article's DNA!
The rules for DOIs have been updated in the 7th edition of the Publication Manual of the American Psychological Association. They should be included as URLs, rather than just the alphanumeric string.
DOI: If a journal article has a Digital Object Identifier (DOI) listed, you will always include this identifier in your reference as a URL.
Online Database: For works from databases that publish works of limited circulation (such as the ERIC database) or original, proprietary material available only in that database (such as UpToDate), include the name of the database or archive and the URL of the work. If the URL requires a login or is session specific, meaning it will not resolve for readers, provide the URL of the database or specific archive home page or login page instead of the URL for the work.
Print: If you viewed a journal article in its print format, be sure to check if it has a DOI listed. If it does not, your reference to the article would end after you provide the page range of the article.
Date: When possible, include the year, month, and date in references. If the month and date are not available, use the year of publication.
ePub Ahead of Print articles, also labeled Advanced Online Publication articles, may not have a volume number, issue number, or page numbers assigned to them. If you cannot find a fully published version of the article that includes this information, you can cite the article as an advanced online publication, noting its status where you would usually include the volume, issue, and page numbers. If possible, update your reference to the final version of the source when it becomes available.
Muldoon, K., Towse, J., Simms, V., Perra, O., & Menzies, V. (2012). A longitudinal analysis of estimation, counting skills, and mathematical ability across the first school year. Developmental Psychology. Advance online publication. https://doi.org/10.1037/a0028240