Since the Digital Object Identifier (DOI) system was introduced in 2000, guidelines on how to best display DOIs have evolved.Effective March 2017, Crossref, an influential DOI registration agency, nowrecommendsthe following format:

https://doi.org/10.1037/rmh0000008

Note the use of "https" instead of "http", and "doi.org" instead of "dx.doi.org".

While the 6th edition of thePublication Manual of the American Psychological Association, published in 2010, recommended the originaldoi:10.1037/rmh0000008format, APA hasupdated their guidelinesto follow the Crossref guidelines for displaying DOIs with this latest format.

The CSL styles for the 6th edition of APA has therefore been updated to use thehttps://doi.org/10.1037/rmh0000008format as well.

As Crossrefexplainsin their guidelines, the original concisedoi:10.1037/rmh0000008format was recommended with the hope that web browsers would one day automatically recognize and hyperlink these DOIs.

Since this didn't happen, Crossrefchanged its recommendationin 2011 to show DOIs as regular URLs instead, in the formathttp://dx.doi.org/10.1037/rmh0000008.APA started to recommend this newer (but nowadays also outdated) format in its 2012 companion guide,APA Style Guide to Electronic References, and discussed this change in a 2014blog post.

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 shorterdoi.orginstead ofdx.doi.org.Together, this let Crossrefchangeits recommended format tohttps://doi.org/10.1037/rmh0000008.