by Jeff Hume-Pratuch

In the sixth edition of the APA Publication Manual, DOIs are formatted according to the initial recommendations from CrossRef:

Herbst, D. M., Griffith, N. R., & Slama, K. M. (2014). Rodeo
cowboys: Conforming to masculine norms and help-
seeking behaviors for depression. Journal of Rural
Mental Health, 38, 20–35. doi:10.1037/rmh0000008

The DOI prefix (10.1037, in the case of APA journals) is a unique number of four or more digits assigned to organizations; the suffix (rmh0000008) is assigned by the publisher and identifies the journal and individual article.

Recently, however, CrossRef changed the format of the DOI to a more user-friendly one in the form of a URL:

Herbst, D. M., Griffith, N. R., & Slama, K. M. (2014). Rodeo
cowboys: Conforming to masculine norms and help-
seeking behaviors for depression. Journal of Rural
Mental Health, 38, 20–35. http://dx.doi.org/10.1037
/rmh0000008

As you can see, the DOI itself is the same (10.1037/rmh0000008), but it is preceded by http://dx.doi.org/ to insure that it resolves into a working link. Because this change is recent and many publishers are still implementing the new CrossRef guidelines, either the old or the new DOI format is acceptable. But be sure not to mush them together! Here are some examples.

Correct:
•doi:10.1037/rmh0000008
•http://dx.doi.org/10.1037/rmh0000008

Incorrect:
•http://doi:10.1037/rmh0000008
•doi:http://dx.doi.org/10.1037/rmh0000008
•Retrieved from http://dx.doi.org/10.1037/rmh0000008

Source: APA Style Blog