Since the Digital Object Identifier (DOI) system was introduced in 2000, guidelines on how to best display DOIs have kept evolving. In late 2016, Crossref, an influential DOI registration agency, announced it would change its official recommendation to the following format:

https://doi.org/10.1037/rmh0000008

The 6th edition of the Publication Manual of the American Psychological Association, published in 2010, still recommends the original doi:10.1037/rmh0000008 format. However, in 2012, APA published a companion guide, APA Style Guide to Electronic References, in which APA started to recommend the newer (but nowadays also outdated) http://dx.doi.org/10.1037/rmh0000008 format. Finally, APA has indicated that newer formats are acceptable, and that they tend to follow the Crossref guidelines. In view of this, the CSL style for the 6th edition of APA has been updated to use the https://doi.org/10.1037/rmh0000008 format currently recommended by Crossref.

As Crossref explains in their blog post on their most recent recommendation, the original concise doi:10.1037/rmh0000008 format was recommended with the hope that web browsers would one day automatically recognize and hyperlink these DOIs.

Since this didn't happen, Crossref changed its recommendation in 2011 to show DOIs as regular URLs instead, in the format http://dx.doi.org/10.1037/rmh0000008.

More recently, there has been a strong movement to move the web over from HTTP to the more secure HTTPS protocol. Technical changes also made it possible to link DOIs via the shorter doi.org instead of dx.doi.org. Together, this changed the recommended format to the currently preferred https://doi.org/10.1037/rmh0000008.

In addition to their manuals, APA published a blog post in 2014 in which they discussed the change from the doi: to the http://dx.doi.org format.

In 2015, APA also indicated that they have no objection to the shorter http://doi.org format:

This DOI world is constantly changing, and APA formulated its guideline to use the http://dx.doi.org prefix based on the recommendation of CrossRef.org. CrossRef still specifies that this is the format to use; I am unaware as to whether they know that the doi.org site suggests a simpler format. Certainly as long as the DOI resolves you have satisfied the purpose of the reference, and in the future I wouldn’t be surprised if all publishers officially endorsed the shorter form. In the meantime, if you want to be a stickler for the rules, the dx.doi format is the one that’s officially endorsed.

Best regards,

The APA Style Expert Team