"Errors can creep into citations in many ways, including import of incorrect citations from another source, mispelling of author names, or simple miskeying. DOIs are particularly vulnerable to miskeying, due to their length and meaninglessness. One of my sources estimates that 20% of author keyed DOIs in citations are incorrect! If you have the opportunity to decide on the form of a DOI, don't forget to consider the human factor.
It's hard to get estimates of the current error rate in citation metadata; when I was producing an electronic journal ten years ago, my experience was consonant with industry lore that said that 10% of author-supplied citations were incorrect in some way. My guess, based on a few conversations and a small number of experiments, is that a typical error rate in published citations is 1-3%. A number of processes are pushing this number down, most of them connected with citation linking in some way."
- Eric Hellman, "Publish-Before-Print and the Flow of Citation Metadata"