https://www.iastatedigitalpress.com/jlsc/article/id/16288/
"Introduction: Digital preservation underpins the persistence of scholarly links and citations through the digital object identifier (DOI) system. We do not currently know, at scale, the extent to which articles assigned a DOI are adequately preserved."

"Results: Of the 7,438,037 works examined, there were 5.9 million copies spread over the archives used in this work. Furthermore, a total of 4,342,368 of the works that we studied (58.38%) were present in at least one archive. However, this left 2,056,492 works in our sample (27.64%) that are seemingly unpreserved. The remaining 13.98% of works in the sample were excluded either for being too recent (published in the current year), not being journal articles, or having insufficient date metadata for us to identify the source."