"The sample of DOIs included in the study was made up of a random selection of up to 1,000 registered to each member organization. Twenty-eight percent of these works — more than two million articles — did not appear in a major digital archive, despite having an active DOI. Only 58% of the DOIs referenced works that had been stored in at least one archive. The other 14% were excluded from the study because they were published too recently, were not journal articles or did not have an identifiable source."
(Photo: Anna Berkut/Alamy).