When I'm casually browsing through bibliography section of preprints, sometimes I find that an author will also include the DOI information in the citation.
For example, I just picked a random Arxiv paper from today: https://arxiv.org/pdf/2207.06887.pdf
Observe that in the citation section, some references have a DOI attached to it, but others do not.
I've observed this in many preprints and publications.
- Is there a good reason to add the DOI information?
- Why is it that sometimes certain references have DOI information, but others do not? Is this a citation consistency issue?