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. You will not have to include the URL of the journal's home page or of the database from which you retrieved the article if a DOI is available.
Online Database: If you viewed a journal article in an online database and it does not have a DOI, you will need to do a quick search outside of the database to locate the URL for the journal's home page. This information must be included in the reference. If the journal is no longer being published and it does not have a home page, then include the URL for the home page of the database from which you retrieved the article.
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://dx.doi.org/10.1037/