It is a fundamental part of the PILA agreement that is signed when a publisher joins CrossRef that they will link to other articles using their DOIs. So, for example, if I cite an article in a journal that has a DOI, I must ensure that I use that DOI. If it doesn't have a DOI, then I needn't link to the article using the DOI.
Martin Paul Eve (Tue,) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: